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Unformatted text preview: STAT 210 FOCUS EXERCISE 9 The parameter of interest is the mean cost of all new textbooks used in Virginia institutions of higher education. Data for all new textbooks is not available to us, and hence the mean cost of all new textbooks used in Virginia institutions of higher education must be estimated. Assume that it is known that the standard deviation of costs of all new textbooks is $13.50. 1. To estimate the mean cost of all new textbooks used in Virginia institutions of higher education, you are asked to compute a 95% confidence interval estimate. You should be very specific with your estimate by creating an interval whose width does not exceed $10.00. How large of a sample of new textbooks used in Virginia institutions of higher education would you need to select in order for a 95% confidence interval estimate to achieve this? Xbar +/ 5.0 Xbar +/ 1.960 (13.50 / sqrt N) 5.0 = 1.960 (13.50 / sqrt N) N = 29 2. Upon seeing the answer computed in problem 1 and not knowing the shape of the distribution, a simple...
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 Fall '06
 Basu

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