A survey is planned to determine the ^HSI mean annual family medical expenses of employees of a large company. The management of the company wishes to be 95% confident that the sample mean is correct to within ±$50 of the population mean annual family medical expenses. A previous study indicates that the standard deviation is approximately $400.
a. How large a sample is necessary?
b. If management wants to be correct to within ±$25, how many employees need to be selected?