10.54 Mileage of midsized cars The following table lists the fuel economy of 15 midsized cars when driven in the city and when driven on the highway, along with their overall mileage. Their performance in miles per gallon (mpg) in each test was recorded and the means and standard deviations of their gas mileage were obtained.

a. Estimate the change in the mean overall performance as compared to the mean value of performance in the city.

b. Is this information sufficient to find a confidence interval or conduct a test about the change in the mean? If not, what else do you need to know?

c. What assumptions are necessary for the inference in part b?

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Std. Dev. Mean Overall (mpg) 4.58 30.4 City (mpg) 6.03 21.47 Highway (mpg) 2.50 40.87