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Academic Support AP Statistics Unit 2: Probability, Random Variables, and Probability Distributions

Random Variables: Discrete vs Continuous, Distributions, and Examples

Learn random variable with current AP Statistics scope, proper formulas, worked examples, and original Easy, Tough, and Toughest questions.

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Concept Lesson

Random Variables: Discrete vs Continuous, Distributions, and Examples

A lesson in discrete and continuous random variables that moves from intuition and definitions to worked reasoning, error correction, and independent practice.

Course status: Revised 2026-27 course
Updated: July 18, 2026
Practice: Easy, Tough and Toughest

Lesson Goals: Random Variable

A random variable maps outcomes to numbers; a discrete distribution assigns probabilities that sum to one, while a continuous density assigns probability through area over intervals.

Reader tasksupport, probability distributions, density, cumulative probability, and notation
Planned modules8
Mathematics2 expressions
Worked checks42

Boundary: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

Definition

Definition in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Definition in random variable, A constructed discrete random variable for a city bus arrival investigation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Definition in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Definition in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Discrete random variables

Discrete random variables in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Discrete random variables in random variable, A constructed discrete random variable for a water-filtration experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for discrete random variables.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Discrete random variables in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Discrete random variables in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Continuous random variables

Continuous random variables in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Continuous random variables in random variable, A constructed discrete random variable for a quality-control inspection has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for continuous random variables.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Continuous random variables in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Continuous random variables in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Probability distributions

Probability distributions in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Probability distributions in random variable, A constructed discrete random variable for a public-parks visitor survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for probability distributions.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Probability distributions in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Probability distributions in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Valid distribution conditions

Valid distribution conditions in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Valid distribution conditions in random variable, A constructed discrete random variable for a school library checkout study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for valid distribution conditions.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Valid distribution conditions in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Valid distribution conditions in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Examples

Examples in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Examples in random variable, A constructed discrete random variable for a school library checkout study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Examples in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Examples in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Transformations

Transformations in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Transformations in random variable, A constructed discrete random variable for a commuter route study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for transformations.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Transformations in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Transformations in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Practice

Practice in random variable: The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.

Worked reasoning

For Practice in random variable, A constructed discrete random variable for a quality-control inspection has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for practice.

xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.

When the idea is valid

For Practice in random variable, List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

Misconception to remove

For Practice in random variable, reject this error: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Formula and Notation Reference

Discrete probability total

xp(x)=1

Discrete probability total in Random Variable: This expression belongs specifically to discrete and continuous random variables; define every symbol and apply the scope rule for support, probability distributions, density, cumulative probability, and notation before calculation.

Continuous interval probability

P(a<X<b)=abf(x)dx

Continuous interval probability in Random Variable: Define the event or random variable first; complements, conditioning, and trial assumptions determine which probability expression applies.

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Guided, Independent and Challenge Practice

Every question in Random Variables: Discrete vs Continuous, Distributions, and Examples is newly written from the revised framework and the logic visible in public College Board materials. Constructed numerical settings are identified as instructional scenarios and are never represented as measurements from a real population. No released or secure question wording is reproduced.

Easy Practice

Easy 1: Definition

Question P43-Easy-1. A constructed discrete random variable for a seedling-growth comparison has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

Worked solution and validity check

Worked solution P43-Easy-1. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 2: Discrete random variables

Question P43-Easy-2. A constructed discrete random variable for a website response-time study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for discrete random variables.

Worked solution and validity check

Worked solution P43-Easy-2. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 3: Continuous random variables

Question P43-Easy-3. A constructed discrete random variable for a classroom memory study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for continuous random variables.

Worked solution and validity check

Worked solution P43-Easy-3. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 4: Probability distributions

Question P43-Easy-4. A constructed discrete random variable for a recycling-behavior survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for probability distributions.

Worked solution and validity check

Worked solution P43-Easy-4. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 5: Valid distribution conditions

Question P43-Easy-5. A constructed discrete random variable for a battery-life laboratory trial has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for valid distribution conditions.

Worked solution and validity check

Worked solution P43-Easy-5. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 6: Examples

Question P43-Easy-6. A constructed discrete random variable for a recycling-behavior survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

Worked solution and validity check

Worked solution P43-Easy-6. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 7: Transformations

Question P43-Easy-7. A constructed discrete random variable for a public-parks visitor survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for transformations.

Worked solution and validity check

Worked solution P43-Easy-7. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 8: Practice

Question P43-Easy-8. A constructed discrete random variable for a commuter route study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for practice.

Worked solution and validity check

Worked solution P43-Easy-8. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 9: Definition

Question P43-Easy-9. A constructed discrete random variable for a reading-speed investigation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

Worked solution and validity check

Worked solution P43-Easy-9. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 10: Discrete random variables

Question P43-Easy-10. A constructed discrete random variable for a campus dining survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for discrete random variables.

Worked solution and validity check

Worked solution P43-Easy-10. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 11: Continuous random variables

Question P43-Easy-11. A constructed discrete random variable for a package-delivery sample has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for continuous random variables.

Worked solution and validity check

Worked solution P43-Easy-11. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 12: Probability distributions

Question P43-Easy-12. A constructed discrete random variable for a public-parks visitor survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for probability distributions.

Worked solution and validity check

Worked solution P43-Easy-12. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 13: Valid distribution conditions

Question P43-Easy-13. A constructed discrete random variable for a package-delivery sample has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for valid distribution conditions.

Worked solution and validity check

Worked solution P43-Easy-13. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Easy 14: Examples

Question P43-Easy-14. A constructed discrete random variable for a water-filtration experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

Worked solution and validity check

Worked solution P43-Easy-14. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough Practice

Tough 1: Probability distributions

Question P43-Tough-1. A constructed discrete random variable for a seedling-growth comparison has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for probability distributions.

Worked solution and validity check

Worked solution P43-Tough-1. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 2: Valid distribution conditions

Question P43-Tough-2. A constructed discrete random variable for a greenhouse germination experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for valid distribution conditions.

Worked solution and validity check

Worked solution P43-Tough-2. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 3: Examples

Question P43-Tough-3. A constructed discrete random variable for a tutoring-program evaluation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

Worked solution and validity check

Worked solution P43-Tough-3. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 4: Transformations

Question P43-Tough-4. A constructed discrete random variable for a battery-life laboratory trial has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for transformations.

Worked solution and validity check

Worked solution P43-Tough-4. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 5: Practice

Question P43-Tough-5. A constructed discrete random variable for a seedling-growth comparison has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for practice.

Worked solution and validity check

Worked solution P43-Tough-5. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 6: Definition

Question P43-Tough-6. A constructed discrete random variable for a city bus arrival investigation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

Worked solution and validity check

Worked solution P43-Tough-6. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 7: Discrete random variables

Question P43-Tough-7. A constructed discrete random variable for a commuter route study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for discrete random variables.

Worked solution and validity check

Worked solution P43-Tough-7. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 8: Continuous random variables

Question P43-Tough-8. A constructed discrete random variable for a public-parks visitor survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for continuous random variables.

Worked solution and validity check

Worked solution P43-Tough-8. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 9: Probability distributions

Question P43-Tough-9. A constructed discrete random variable for a tutoring-program evaluation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for probability distributions.

Worked solution and validity check

Worked solution P43-Tough-9. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 10: Valid distribution conditions

Question P43-Tough-10. A constructed discrete random variable for a classroom memory study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for valid distribution conditions.

Worked solution and validity check

Worked solution P43-Tough-10. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 11: Examples

Question P43-Tough-11. A constructed discrete random variable for a water-filtration experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

Worked solution and validity check

Worked solution P43-Tough-11. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 12: Transformations

Question P43-Tough-12. A constructed discrete random variable for a commuter route study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for transformations.

Worked solution and validity check

Worked solution P43-Tough-12. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 13: Practice

Question P43-Tough-13. A constructed discrete random variable for a website response-time study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for practice.

Worked solution and validity check

Worked solution P43-Tough-13. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Tough 14: Definition

Question P43-Tough-14. A constructed discrete random variable for a website response-time study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

Worked solution and validity check

Worked solution P43-Tough-14. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest Practice

Toughest 1: Examples

Question P43-Toughest-1. A constructed discrete random variable for a campus dining survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

Worked solution and validity check

Worked solution P43-Toughest-1. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 2: Transformations

Question P43-Toughest-2. A constructed discrete random variable for a school library checkout study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for transformations.

Worked solution and validity check

Worked solution P43-Toughest-2. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 3: Practice

Question P43-Toughest-3. A constructed discrete random variable for a seedling-growth comparison has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for practice.

Worked solution and validity check

Worked solution P43-Toughest-3. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 4: Definition

Question P43-Toughest-4. A constructed discrete random variable for a battery-life laboratory trial has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

Worked solution and validity check

Worked solution P43-Toughest-4. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 5: Discrete random variables

Question P43-Toughest-5. A constructed discrete random variable for a package-delivery sample has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for discrete random variables.

Worked solution and validity check

Worked solution P43-Toughest-5. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 6: Continuous random variables

Question P43-Toughest-6. A constructed discrete random variable for a city bus arrival investigation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for continuous random variables.

Worked solution and validity check

Worked solution P43-Toughest-6. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 7: Probability distributions

Question P43-Toughest-7. A constructed discrete random variable for a commuter route study has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for probability distributions.

Worked solution and validity check

Worked solution P43-Toughest-7. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 8: Valid distribution conditions

Question P43-Toughest-8. A constructed discrete random variable for a greenhouse germination experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for valid distribution conditions.

Worked solution and validity check

Worked solution P43-Toughest-8. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 9: Examples

Question P43-Toughest-9. A constructed discrete random variable for a greenhouse germination experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for examples.

Worked solution and validity check

Worked solution P43-Toughest-9. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 10: Transformations

Question P43-Toughest-10. A constructed discrete random variable for a water-filtration experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for transformations.

Worked solution and validity check

Worked solution P43-Toughest-10. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 11: Practice

Question P43-Toughest-11. A constructed discrete random variable for a seedling-growth comparison has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for practice.

Worked solution and validity check

Worked solution P43-Toughest-11. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 12: Definition

Question P43-Toughest-12. A constructed discrete random variable for a tutoring-program evaluation has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for definition.

Worked solution and validity check

Worked solution P43-Toughest-12. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 13: Discrete random variables

Question P43-Toughest-13. A constructed discrete random variable for a public-parks visitor survey has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for discrete random variables.

Worked solution and validity check

Worked solution P43-Toughest-13. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Toughest 14: Continuous random variables

Question P43-Toughest-14. A constructed discrete random variable for a greenhouse germination experiment has values [0, 1, 2, 4] with probabilities [0.2, 0.35, 0.3, 0.15]. Verify the distribution and find P(X2) for continuous random variables.

Worked solution and validity check

Worked solution P43-Toughest-14. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. xp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45. Interpretation: The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. Validity: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X. Error to reject: A continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

AP Response and Publication Checklist

Audit pointRequired evidence for random variable
ScopeP44 owns mean and standard deviation calculations; P45 owns binomial structure.
Method or sourceA random variable maps outcomes to numbers; a discrete distribution assigns probabilities that sum to one, while a continuous density assigns probability through area over intervals.
Calculationxp(x)=0.20+0.35+0.30+0.15=1.00,P(X2)=0.30+0.15=0.45.
InterpretationThe random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value.
ValidityList the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.
CorrectionA continuous random variable has probability zero at any single exact value even though intervals can have positive probability.

Frequently Asked Questions

How does definition work in random variable?

Answer for random variable and Definition. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. The required validity evidence is: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

How does discrete random variables work in random variable?

Answer for random variable and Discrete random variables. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. The required validity evidence is: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

How does continuous random variables work in random variable?

Answer for random variable and Continuous random variables. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. The required validity evidence is: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

How does probability distributions work in random variable?

Answer for random variable and Probability distributions. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. The required validity evidence is: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

How does valid distribution conditions work in random variable?

Answer for random variable and Valid distribution conditions. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. The required validity evidence is: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

How does examples work in random variable?

Answer for random variable and Examples. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. The required validity evidence is: List the support completely and distinguish a probability mass function for discrete X from area under a density for continuous X.

How does discrete random variable connect to Random Variable?

discrete random variable within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Definition, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

How does variable and random variable connect to Random Variable?

variable and random variable within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Discrete random variables, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

How does continuous random variable connect to Random Variable?

continuous random variable within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Continuous random variables, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

How does what is a random variable connect to Random Variable?

what is a random variable within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Probability distributions, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

How does discrete random variables connect to Random Variable?

discrete random variables within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Valid distribution conditions, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

How does what random variable connect to Random Variable?

what random variable within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Examples, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

How does random variables connect to Random Variable?

random variables within random variable. The distribution is valid because all probabilities are nonnegative and sum to 1; P(X2)=0.45. The random variable maps each outcome of the process to a numerical value; its distribution assigns long-run probability to each possible value. For Transformations, the controlling scope is: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

Sources

Administrative and curricular statements in Random Variables: Discrete vs Continuous, Distributions, and Examples were checked on July 18, 2026. The linked College Board pages control any later policy change; all instructional datasets in original questions are explicitly constructed rather than attributed to a real study.

Random Variable Conclusion

A random variable maps outcomes to numbers; a discrete distribution assigns probabilities that sum to one, while a continuous density assigns probability through area over intervals. Mastery of random variable therefore requires the exact evidence, mathematics, interpretation, and scope developed in this guide, while preserving this boundary: P44 owns mean and standard deviation calculations; P45 owns binomial structure.

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