Question

You need to estimate the mean number of travel days per year for outside salespeople. The mean of a small pilot study was 160 days, with a standard deviation of 25 days. If you must estimate the population mean within 3 days, how many outside salespeople should you sample? Use the 98% confidence level.

Answer 1

Solution =

Given ,

= 25    ..Population SD

E = 3 Margin of error

c = 98% = 0.98 ...confidence level

Find sample size required.

c = 0.98

= 1- c = 1- 0.98 = 0.02

  /2 = 0.01

Using Z table ,

= 2.326

Now, sample size (n) is given by,

=  {(2.326 * 25 ) / 3 }2

= 375.7136

= 376 ..(round to the next whole number)

Answer : Required Sample size is n = 376