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 (mpg) gasoline mileage with booster-X2

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

What critical value should be used at = 0.05? options:

a. 2.447

b. 2.365

c 1.943

d. 1.895