A statistics professor wants to compare today\'s students with those 25 years ag

Question

A statistics professor wants to compare today's students with those 25 years ago. All of his current students' marks are stored on a computer so that he can easily determine the population mean. However the marks 25 years ago reside only in his musty files He does not want to retrieve all the marks and will be satisfied with a 95% confidence interval estimate of the mean mark 25 years ago. If he assumes that the population standard deviation is 13, how large a sample should he take to estimate the mean to within 3 marks? Sample Size = _________________

Explanation / Answer

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) = 13
ME =3
n = ( 1.96*13/3) ^2
= (25.48/3 ) ^2
= 72.14 ~ 73      

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