A fast food restaurant located in a commercial district of a city has developed an improved process for serving customers during the noon-to-1:00 p.m. lunch period. The waiting time (defined as the time the customer enters the line until he or she reaches the front of the line) of all customers during this hour is recorded over a period of 1 week. A random sample of 15 customers is selected, and the results are as follows:

4.21 5.55 3.02 5.13 4.77 2.34 3.54 3.20

4.50 6.10 0.38 5.12 6.46 6.19 3.79

a. At the 0.05 level of significance, is there evidence that the mean waiting time is less than 5 minutes?

b. What assumption must hold in order to perform the test in (a)?

c. Evaluate the assumption in (b) through a graphical approach. Discuss.

d. As a customer walks into the restaurant during the lunch hour, she asks the manager how long she can expect to wait. The manager replies, almost certainly not longer than 5 minutes. On the basis of the results of (a), evaluate this statement.