You need to estimate the mean number of travel days per year

You need to estimate the mean number of travel days per year for outside salespeople. The mean of a small pilot study was 150 days, with a standard deviation of 36 days.

If you must estimate the population mean within 6 days, how many outside salespeople should you sample? Use the 95% confidence level. (Use Student\'s z Distribution Table.) (Round up your answer to the next whole number.)

Solution

For 95%, z = 1.96

d=6

sd=36

Sample size = (z² * s²)/d²

= (1.96² * 36²)/6²

=138.2976

The sample size required= 139