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Chapter 11 Exercise

# Chapter 11 Exercise - 0.5 inches or less To test their...

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Sample Questions Chapter 11 1. A sample of 15 items provides a sample mean of 18 and a sample variance of 16. Compute a 95% confidence interval estimate for the standard deviation of the population. ANSWER: 2.93 to 6.31 (rounded) 2. A random sample of 25 employees of a local utility firm showed that their monthly incomes had a sample standard deviation of \$112. Provide a 90% confidence interval estimate for the standard deviation of the incomes for all the firm's employees. ANSWER: 90.93 to 147.43 (rounded) 3. A random sample of 41 scores of students taking the ACT test showed a standard deviation of 8 points. Provide a 98% confidence interval estimate for the standard deviation of all the ACT test scores. ANSWER: 6.34 to 10.74 (rounded) 4. A sample of 61 items provided a sample mean of 932, a sample mode of 900, and a sample standard deviation of 11. Test the following hypotheses using a = 0.05. What is your conclusion? H 0 : s 2 80 H a : s 2 > 80 ANSWER: c 2 = 90.75 > 83.2976; reject Ho. 5. A lumber company has claimed that the standard deviation for the lengths of their 6 foot boards is
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Unformatted text preview: 0.5 inches or less. To test their claim, a random sample of 17 six-foot boards is selected; and it is determined that the standard deviation of the sample is 0.43. Do the results of the sample support the company's claim? Use a = 0.1. ANSWER: Since c 2 = 11.83 < 23.54, do not reject Ho. 6. At a = 0.1, test to see if the population variances from which the following samples were drawn are equal. Group 1 Group 2 n 1 = 21 n 2 = 19 s 1 = 18 s 2 = 16 ANSWER: Since F = 1.26 < 2.19, do not reject Ho. 7. The standard deviation of the ages of a sample of 16 executives from the northern states was 8.2 years; while the standard deviation of the ages of a sample of 25 executives from the southern states was 12.8 years. At a = 0.1, test to see if there is any difference in the standard deviations of the ages of all the northern and southern executives. ANSWER: Since F = 2.44 > 2.29, reject Ho....
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