A statistics professor would like to set the difficulty for an exam such that 90% of the 170 students writing complete it in less than 2.5 hours.To estimate the difficulty ahead of delivery, 4 proxies completed the exam beforehand with a mean time of 2.2 hours and a standard error of 0.3 hours.

Question

If the sample is taken to be representative of the population, would you expect 90% of students to complete the exam in under 2.5 hours? (show work).