A tire manufacturer is interested in testing the fuel economy for two different tread patterns. Tires of each tread type were driven for 1000 miles on each of 9 different cars. The mileages, in miles per gallon, were as follows:

a. Construct a 95% confidence interval for the mean difference in fuel economy.

b. Based on the confidence interval, is it reasonable to believe that the mean mileage may be the same for both types of tread?

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Car Tread A Tread B 1 24.7 20.3 2 22.5 19.0 3 24.0 22.5 4 26.9 23.1 5 22.5 20.9 6 23.5 23.6 7 22.7 21.4 68 19.7 18.2 27.5 25.9