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


Determine the mean of the differences.

A) -1.67
B) -1.43
C) 1.67
D) 6.3