[EX09-033] The fuel economy information on a new SUV window sticker indicates that its new owner can expect 16 mpg (miles per gallon)

in city driving and 20 mpg for highway driving and 18 mpg overall. Accurate gasoline records for one such vehicle were kept, and a random sample of mileage per tank of gasoline was collected: 

17.6 17.7 

18.1 22.0 

17.0 19.4 

18.9 17.4 

21.0 19.2 

18.3 19.1 

20.7 16.7 

19.4 18.2 18.4 17.1 17.4 15.8 17.9 18.0 16.3 17.5 17.3 20.4 19.1 21.0 18.1 19.0 19.6 18.9 16.8 18.2 17.6 19.1 18.0 16.8 20.9 17.9 17.7 20.3 18.6 19.0 16.5 19.4 18.6 18.6 17.3 18.7

a. Determine whether an assumption of normality is reasonable. Explain.

b. Construct a 95% confidence interval for the estimate of the mean mileage per gallon.

c. What does the confidence interval suggest about SUVs’ fuel economy expectations as expressed on the window sticker?