A Researcher Wanted to Determine If Using an Octane Booster $X _ { 1 }$

Multiple Choice

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. Consequently, $D = X _ { 1 } - X _ { 2 }$ .


What critical value should be used at $\alpha = 0.05 ?$

A) -1.943
B) -2.447
C) -2.365
D) -1.895