Baggage fees charged by airlines have received much attention recently as the industry has looked for ways to increase revenue without directly increasing fares. American Airlines would like to investigate if the average number of bags checked per flight fell after the company implemented fees for checking them. The following table shows the average numbers of checked bags per flight for a random sample of Boeing 737 domestic flights both before and after the fees were implemented. The population standard deviations and sample sizes are also indicated.

a. Perform a hypothesis test using α = 0.10 to determine if the average number of checked bags decreased after the checked baggage fees were administered.

b. Determine the p value and interpret the results.

c. Construct a 90% confidence interval to estimate the difference in the average number of checked bags per flight before and after the fees were implemented.

d. Verify your results using PHStat.

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Before Sample mean Sample size Population standard deviation After 109.7 50 9.4 42