Question

In order to test the effect of Gasohol on mileage, a research agency randomly selected two compact cars (same model) from each of four major manufacturers. Gasohol was used in one of each type of car and unleaded used in the rest. The mileage results for each car-fuel combination are given below.

Car	Gasohol	Unleaded
Dodge	31.5 mpg	30.3 mpg
Chevy	28.9 mpg	31.2 mpg
Ford	34.5 mpg	32.8 mpg
VW	37.2 mpg	35.7 mpg

We would like to construct a 95% confidence interval for the difference in average mileage between gasohol and unleaded gasoline.

1. Construct the confidence interval assuming the population of differences of gas mileages is normal.

Answer 1