A researcher wanted to determine if using an octane booster would increase gasoline mileage. A random sample of seven cars was selected; the cars were driven for two weeks without the booster and two weeks with the booster. Use the definitions of X 1 and X 2 as given in the table and find the test value to test the researcher's hypothesis at = 0.05.

Gasoline mileage Gasoline mileage Without booster, X1 mpg With booster X2 mpg 21.2 23.8

25.4 25.6

20.9 22.4

27.6 28.3

22.8 24.5

27.3 28.8

23.4 25.2