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 90% 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 $369.
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?