Given that you have a starting standard time for a job of ni

Given that you have a starting standard time for a job of ninety(90) minutes with a standard deviation of 10 minutes:

A) If you want to be 95% confident that you are within 10% of the true time, how many samples must you take?

Solution

Compute Sample Size
n = (Z a/2 * S.D / ME ) ^2
Z/2 at 0.05% LOS is = 1.96 ( From Standard Normal Table )
Standard Deviation ( S.D) = 10
ME = 10% of True Time = 10% of 90 = 9
n = ( 1.96*10/9) ^2
= (19.6/9 ) ^2
= 4.743 ~ 5