Question: The Qwest Communications Company is interested in estimating the average number of minutes its customers spend on long distance calls per month. The company wants the estimate made with 96% confidence and a margin of error of no more than 3 minutes.

a. A previous research showed that the standard deviation for long distance phone call is 18 minutes per month. What should be the required sample size?

b. Company records indicate that the longest long distance call recorded was 136 minutes. The shortest long distance was considered to be zero minutes. Calculate the sample size required to estimate the average long distance calls.