The file P08_07.xlsx contains a random sample of 200 service times during the busiest hour of the day at a particular fast-food restaurant. Find a 95% confidence interval for each of the following population parameters. Then explain how each result might be useful to the manager of the restaurant in terms of improving service.
a. The mean service time
b. The standard deviation of service times
c. The proportion of service times longer than 90 seconds
d. The proportion of service times shorter than 60 seconds