If you want to be 95 confident of estimating the population

If you want to be 95% confident of estimating the population mean to within a sampling error of + 0.03, what sample size is needed?

Solution

Compute Sample Size ( n ) =(Z a/2 * S.D / ME ) ^2
Z?/2 at 5% LOS is = 1.96 ( From Standard Normal Table )
Standard Deviation ( S.D) is Unknown
ME =0.03
n = ( 1.96*S.D/0.03) ^2
   = S.D^2*(1.96/0.03) ^2
   = 4268.44*S.D^2