7. The manager of the local Hamburger Express wishes to estimate the mean time customersspend at the drive-through window. A sample of 20 customers experienced amean waiting time of 2.65 minutes, with a standard deviation of 0.45 minutes.

a. Develop a 95 percent confidence interval for the mean waiting time.

b. Show that the margin of error would be smaller for a sample size of 30 customers, other things equal.