 # . In a study of the income of U.S. factory workers, a random sample of 100 workers shows a sample

| November 18, 2015

1. In a study of the income of U.S. factory workers, a random sample of 100 workers shows a sample mean of \$35,000. Assume that the population standard deviation is \$4,500, and that the population is normally distributed.

A) Compute the 90%,95% and 99% confidence intervals for the unknown population mean.

B) Briefly discuss what happens to the width of the interval estimate as the confidence level increases. Why does this seem reasonable?

2. In a study of the starting salary of college graduates with degrees in Accounting, a random sample of 40 graduates shows a sample mean of \$36,000 and a sample standard deviation of \$2,500. Assume that the population is normally distributed.

A) Compute and explain a 95% confidence interval estimate of the population mean starting salary for Accounting graduates.

3. A telephone poll of 900 American adults asked “where would you rather go in your spare time?”  One response, by 250 adults, was “a movie”. Compute and explain a 95% confidence interval estimate of the proportion of all American adults who would respond “a movie”.

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