Dr wants to estimate the average amount of time students tak

Dr. wants to estimate the average amount of time students take to get from one class to the next. He wants to be able to assert with a 90% confidence that the error is at ost .25 minutes (for a width of 0.5). If it can be presumed from experience that the distribution of time is approx. normal and that standard deviation (sigma) = 1.4 minutes, how many students need to be timed?

Solution

Compute Sample Size
n = (Z a/2 * S.D / ME ) ^2
Z/2 at 0.1% LOS is = 1.64 ( From Standard Normal Table )
Standard Deviation ( S.D) = 1.4
ME =0.25
n = ( 1.64*1.4/0.25) ^2
= (2.296/0.25 ) ^2
= 84.346 ~ 85