13. FedEx and United Parcel Service (UPS) are the world’s two leading cargo carriers by volume and revenue (The Wall Street Journal, January 27, 2004). According to the Airports Council International, the Memphis International Airport (FedEx) and the Louisville International Airport (UPS) are two of the ten largest cargo airports in the world. The following random samples show the tons of cargo per day handled by these airports. Data are in thousands of tons.

Memphis 9.1 15.1 8.8 10.0 7.5 10.5 8.3 9.1 6.0 5.8 12.1 9.3 Louisville 4.7 5.0 4.2 3.3 5.5 2.2 4.1 2.6 3.4 7.0

a. Compute the sample mean and sample standard deviation for each airport.

b. What is the point estimate of the difference between the two population means? Interpret this value in terms of the higher-volume airport and a comparison of the volume difference between the two airports.

c. Develop a 95% confidence interval of the difference between the daily population means for the two airports.