It is desired to estimate the mean number of hours of contin

It is desired to estimate the mean number of hours of continuous use until a certain kind of computer will first require repairs. If it can be assumed than sigma = 48 hours, how large a sample is nedded so that one will be able to assert with 90% confidence that the sample mean is off by at most 10 hours?

Solution

Given a=1-0.9=0.1, Z(0.05) = 1.645 (from standard normal table)

So n=(Z*s/E)^2

=(1.645*48/10)^2

=62.34682

Take n=63