 ## (Solution document) 52 The director of admissions at a large university advises parents of incoming students about the cost of textbooks during a typical semester.

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?

9.54 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?