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 X1 and X2 as given in the table. Consequently D=x1-x2.

gasoline mileage without booster, x1

21.2

25.4

20.9

27.6

22.8

27.3

23.4

gasoline mileage with booster, x2

23.8

25.6

22.4

28.3

24.5

28.8

25.2

State the alternative hypothesis?

Determine the mean of difference?

Compute the standard deviation of the differences?

What critical value should be used at a=0.05?