A Humber nursing student wants to estimate the number of times per year a middle aged woman visits a doctors office. He estimates that the population standard deviation of the number of visits is approximately four, and he wants the estimate to be within two times of the actual mean value. How large a sample should the nurse take to obtain a 95% confidence interval?

(a) What is the critical value that will need to be used to calculate the sample size?

(b) What is the sample size required?