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 91% confidence interval estimate of the mean mark 25
years ago. If he assumes that the population standard deviation
is 11, how large a sample should he take to estimate the mean to within 4 marks?
Sample Size =