Question

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.

Miles / Gal Without	Miles / Gal With
25.02	26.48
23.91	29.39
25.85	29.69
20.27	25.39
24.99	25.81
20.72	28.21
24.39	25.18

Determine the standard deviation of the difference.

		2.621
		4.121
		6.872
		4.121

Answer 1