Your engineering position requires frequent travel to the west coast, typically through Chicago. In reviewing historical airline data, you have determined that over the last year flights into Chicago on Southwest have been normally distributed, arriving an average of 75 minutes late with a standard deviation of 9.8 minutes. Yesterday, a travel agent informed you that Southwest recently changed their scheduling into Chicago and has improved arrival times. To confirm this claim, you collect the arrival times for a random sample of 40 Southwest flights arriving into Chicago, and find a sample mean of 71.6 minutes and a sample standard deviation of 7.2 minutes.

(a) Has there been a change in the mean arrival times on Southwest?
(b) Determine if there been a change in the variability of arrival times on Southwest.
(c) Estimate your arrival time on your next Southwest flight into Chicago with 90% confidence (i. e., give an interval).