Question

You need to estimate the mean number of travel days per year for outside salespeople. The mean of a small pilot study was 140 days, with a standard deviation of 24 days. If you must estimate the population mean within 4 days, how many outside salespeople should you sample? Use the 99% confidence level.

Answer 1

Solution :

Given that,

standard deviation = =24

margin of error = E = 4

At 99% confidence level the z is ,

  = 1 - 99% = 1 - 0.99 = 0.01

/ 2 = 0.01 / 2 = 0.005

Z/2 = Z0.005 = 2.576

Sample size = n = ((Z/2 * ) / E)2

= ((2.576 * 24) / 4)2

= 239

Sample size =239