Worked solution P58-Easy-1. The t interval is (66.140, 74.260). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.20\pm 4.060.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-2. The t interval is (68.343, 76.457). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.40\pm 4.057.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-3. The t interval is (69.601, 77.799). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.70\pm 4.099.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-4. The t interval is (69.688, 76.312). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.00\pm 3.312.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-5. The t interval is (71.109, 78.091). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.60\pm 3.491.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-6. The t interval is (67.054, 73.746). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.40\pm 3.346.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-7. The t interval is (68.601, 75.799). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.20\pm 3.599.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-8. The t interval is (71.171, 77.629). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.40\pm 3.229.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-9. The t interval is (67.034, 74.366). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.70\pm 3.666.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-10. The t interval is (70.717, 77.483). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.10\pm 3.383.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-11. The t interval is (68.643, 75.157). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.90\pm 3.257.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-12. The t interval is (70.117, 75.883). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.00\pm 2.883.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-13. The t interval is (68.160, 73.840). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.00\pm 2.840.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-14. The t interval is (70.306, 77.094). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.70\pm 3.394.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-15. The t interval is (70.240, 75.760). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.00\pm 2.760.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-16. The t interval is (70.140, 78.260). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.20\pm 4.060.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-17. The t interval is (70.286, 78.314). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.30\pm 4.014.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-18. The t interval is (67.735, 74.665). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.20\pm 3.465.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Easy-19. The t interval is (68.864, 75.736). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.30\pm 3.436.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-1. The t interval is (69.693, 77.107). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.40\pm 3.707.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-2. The t interval is (69.513, 77.887). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.70\pm 4.187.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-3. The t interval is (67.428, 75.372). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.40\pm 3.972.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-4. The t interval is (66.567, 74.433). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.50\pm 3.933.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-5. The t interval is (69.168, 76.232). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.70\pm 3.532.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-6. The t interval is (70.415, 77.585). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.00\pm 3.585.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-7. The t interval is (67.931, 74.269). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.10\pm 3.169.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-8. The t interval is (66.725, 73.875). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.30\pm 3.575.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-9. The t interval is (69.159, 76.641). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.90\pm 3.741.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-10. The t interval is (67.654, 74.346). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.00\pm 3.346.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-11. The t interval is (69.960, 76.840). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.40\pm 3.440.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-12. The t interval is (70.333, 77.467). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.90\pm 3.567.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-13. The t interval is (67.676, 73.924). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.80\pm 3.124.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-14. The t interval is (67.721, 73.879). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.80\pm 3.079.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-15. The t interval is (69.305, 74.894). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.10\pm 2.794.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-16. The t interval is (69.805, 77.395). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.60\pm 3.795.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-17. The t interval is (67.456, 75.744). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.60\pm 4.144.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-18. The t interval is (66.851, 73.949). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.40\pm 3.549.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Tough-19. The t interval is (67.688, 74.312). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.00\pm 3.312.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-1. The t interval is (70.363, 78.837). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.60\pm 4.237.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-2. The t interval is (70.570, 79.030). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.80\pm 4.230.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-3. The t interval is (67.735, 74.665). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=71.20\pm 3.465.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-4. The t interval is (69.688, 76.312). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.00\pm 3.312.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-5. The t interval is (70.990, 77.810). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.40\pm 3.410.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-6. The t interval is (70.054, 76.746). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.40\pm 3.346.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-7. The t interval is (66.601, 73.799). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.20\pm 3.599.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-8. The t interval is (67.294, 73.906). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=70.60\pm 3.306.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-9. The t interval is (69.163, 75.437). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.30\pm 3.137.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-10. The t interval is (69.968, 77.032). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.50\pm 3.532.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-11. The t interval is (70.136, 76.064). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.10\pm 2.964.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-12. The t interval is (68.949, 75.651). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.30\pm 3.351.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-13. The t interval is (71.385, 78.415). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.90\pm 3.515.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-14. The t interval is (71.266, 76.934). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.10\pm 2.834.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-15. The t interval is (69.960, 76.239). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.10\pm 3.139.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-16. The t interval is (70.196, 78.404). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.30\pm 4.104.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-17. The t interval is (69.718, 76.882). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=73.30\pm 3.582.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-18. The t interval is (70.197, 77.803). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=74.00\pm 3.803.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.

Worked solution P58-Toughest-19. The t interval is (69.215, 76.585). $$\overline{x}\pm t^{*}\frac{s}{\sqrt{n}}=72.90\pm 3.685.$$ Interpretation: The interval estimates a population mean in the original measurement units and must name the represented population. Validity: Use a random sample or randomized design, independence, and a population shape or sample size that makes the t procedure reliable. Error to reject: Use t rather than z when sigma is unknown and sample standard deviation s estimates it.