Average service time. Recall the drive-thru study in Exercise 7.57 (page 395). Another benchmark that was measured was the service time. A summary of the results (in seconds) for two of the chains is shown here.

Chain n x s Taco Bell 308 158.03 35.7 McDonald’s 317 189.49 42.8

(a) Is there a difference in the average service time between these two chains? Test the null hypothesis that the chains’ average service time is the same. Use a significance level of 0.05.

(b) Construct a 95% confidence interval for the difference in average service time.

(c) Lex plans to go to Taco Bell and Sam to McDonald’s.

Is it true that there is a 95% chance that the interval in part

(b) contains the difference in their service times?

Explain your answer.