A large Midwestern university is interested in estimating th

A large Midwestern university is interested in estimating the mean time that students spend at the student recreation center per week. A previous study indicated that the standard deviation in time is about 40 minutes per week. If the officials wish to estimate the mean time within

Solution

The 90% confidence interval for mean ? is:

[? - 1.645*?/?n , ? + 1.645*?/?n]

We want to have:

1.645*40/?n = 10

Therefore:

(1.645*40/10)^2 = 43.29 -> round this value up: n = 44

So we need 44 samples.