A Company Is Interested in Estimating μ, the Mean Number

Multiple Choice

A company is interested in estimating μ, the mean number of days of sick leave taken by its employees. Their statistician randomly selects 100 personnel files and notes the number of sick days taken by each employee. The sample mean is 12.2 days, and the sample standard deviation is 10 days. How many personnel files would the statistician have to select in order to estimate μ to within 2 days with a 99 percent confidence interval?

A) 2
B) 13
C) 136
D) 165
E) 173