a machine cuts plastic into sheets that are 35 feet 420inche

a machine cuts plastic into sheets that are 35 feet (420inches) long. inches) long. Assume that the population of lengths is normally distributed. a. The company wants to estimate the mean length the machine is cutting the plastic within 0.25 inch. Determine the minimum sample size required to construct a 95% confidence interval for the SD is 0.50 inch

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) = 0.5
ME =0.25
n = ( 1.96*0.5/0.25) ^2
= (0.98/0.25 ) ^2
= 15.37 ~ 16