A researcher is testing the claim that the average university student works less then 15 hours a week. To test this claim she surveys a random sample of 20 undergraduate students who reported an average of 13.5 hours a week of work. We will assume that the population is normally distributed with a standard deviation of 5 hours per week. Test this claim at the alpha of 0.02 by calculating the z-score and comparing it to the critical z-score (z subscript c r i t end subscript equals negative 2.05 right parenthesis.

You have the standard error of the mean, so solve for the z-score.