s=12 =sample sd
= population sd
two-sided normal distribution z-value
Solve to obtain:
n > 30
The mean number of travel days per year for salespeople employed by hardware distributors needs to be estimated with a 98% degree of confidence. For a small pilot study the mean was 150 days and the standard deviation was 12 days. If the population mean is estimated within four days, how many salespeople should be sampled?