Use the Following to Answer Questions

Multiple Choice

Use the following to answer questions
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.
-Determine the mean of the differences.

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