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Unformatted text preview: 128 CHAPTER 8. CONFIDENCE INTERVALS a. Define the Random Variables X and P ’, in words. b. Which distribution should you use for this problem? Explain your choice. c. Construct a 97% confidence interval for the population proportion of people over 50 who ran and died in the same eight–year period. i. State the confidence interval. ii. Sketch the graph. iii. Calculate the error bound. d. Explain what a “97% confidence interval” means for this study. Exercise 8.19 (Solution on p. 136.) In a recent sample of 84 used cars sales costs, the sample mean was $6425 with a standard deviation of $3156. Assume the underlying distribution is approximately normal. a. Which distribution should you use for this problem? Explain your choice. b. Define the Random Variable X , in words. c. Construct a 95% confidence interval for the population average cost of a used car. i. State the confidence interval. ii. Sketch the graph. iii. Calculate the error bound. d. Explain what a “95% confidence interval” means for this study. Exercise 8.20 A telephone poll of 1000 adult Americans was reported in an issue of Time Magazine . One of the questions asked was “What is the main problem facing the country?” 20% answered “crime”. We are interested in the population proportion of adult Americans who feel that crime is the main problem. a. Define the Random Variables X and P ’, in words. b. Which distribution should you use for this problem? Explain your choice. c. Construct a 95% confidence interval for the population proportion of adult Americans who feel that crime is the main problem....
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 Fall '08
 Ripol
 Statistics, Normal Distribution

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