The director of admissions at a large university advises parents of incoming students about the cost of textbooks during a typical semester. He selected a sample of 100 students and recorded their textbook expenses for the semester. He then calculated a sample mean cost of $575.60 and a sample standard deviation of $45.20.

a. Using the 0.10 level of significance, is there evidence that the population mean is above $565?

b. What is your answer in (a) if the standard deviation is $75 and the 0.05 level of significance is used?

c. What is your answer in (a) if the sample mean is $569.60 and the sample standard deviation is $45.20?

You are the manager of a fast-food franchise. Last month the mean waiting time at the counter, as measured from the time a customer places an order until the time the customer receives the order, was 3.7 minutes. The franchise helped you to institute a new process intended to reduce waiting time. You select a random sample of 64 orders. The sample mean waiting time is 3.57 minutes with a sample standard deviation of 0.8 minute. At the 0.05 level of significance, is there evidence that the population mean waiting time is now less than 3.7 minutes?