10.2 Inferences About the Difference Between Two Population Means: a, and a, Unknown 415 a. What is the point estimate of the difference between the mean number of miles that Buffalo residents travel per day and the mean number of miles that Boston residents travel per day? b. What is the 95% confidence interval for the difference between the two popula- tion means? CD file 13. FedEx and United Parcel Service (UPS) are the world's two leading cargo carriers by vol- ume and revenue (The Wall Street Journal, January 27, 2004). According to the Airports Council International, the Memphis International Airport (FedEx) and the Louisville Inter- Cargo national 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 thou- sands of tons. Memphis 9.1 15.1 8.8 10.0 7.5 10.5 6.0 5.8 12.1 03 Louisville 4.7 5.0 4.2 3.3 3.5 2.2 41 2.6 3.4 70 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? In- terpret this value in terms of the higher-volume airport and a comparison of the vol- ume difference between the two airports. c. Develop a 95% confidence interval of the difference between the daily population means for the two airports. 14. Coastal areas of the United States including Cape Cod, the Outer Banks, the Carolinas, and the Gulf Coast had relatively high population growth rates during the 1990s. Data were collected on residents living in the coastal communities as well as on residents living in noncoastal areas throughout the United States (USA Today, July 21, 2000). As- sume that the following sample results were obtained on the ages of individuals in the two populations: Coastal Areas Noncoastal Areas 150 175 39.3 years 35.4 years 16.8 years 15.2 years Test the hypothesis of no difference between the two population means. Use a .05. Formulate the null and alternative hypotheses. What is the value of the test statistic? C. What is the p-value? d. What is your conclusion? 15. Injuries to Major League Baseball players have been increasing in recent years. For the pe- riod 1992 to 2001, league expansion caused Major League Baseball rosters to increase 15%. However, the number of players being put on the disabled list due to injury increased 32% over the same period (USA Today, July 8, 2002). A research question addressed whether Major League Baseball players being put on the disabled list are on the list longer in 2001 than players put on the disabled list a decade earlier