28. Smith Travel Research provides information on the one-night cost of hotel rooms throughout the United States (USA Today, July 8, 2002). Use $2 as the desired margin of error and $22.50 as the planning value for the population standard deviation to find the sample size recommended in (a), (b), and (c).

a. A 90% confidence interval estimate of the population mean cost of hotel rooms

b. A 95% confidence interval estimate of the population mean cost of hotel rooms

c. A 99% confidence interval estimate of the population mean cost of hotel rooms

d. When the desired margin of error is fixed, what happens to the sample size as the confidence level is increased? Would you recommend a 99% confidence level be used by Smith Travel Research? Discuss.