A survey is planned to determine the mean annual family medical expenses of employees of a large company. The management of the company wishes to be 99% confident that the sample mean is correct to within plus or minus $60 of the population mean annual family medical expenses. A previous study indicates that the standard deviation is approximately $276.

a. How large a sample is necessary?

b. If management wants to be correct to within

plus or minus $25, how many employees need to be selected?