To determine the effect of fuel grade on fuel efficiency, 80 new cars of the same make, with identical engines, were each driven for 1000 miles. Forty of the cars ran on regular fuel and the other 40 received premium fuel. The cars with regular fuel averaged 30.2 mpg, with a standard deviation of 1.5 mpg. The cars with premium fuel averaged 31.1 mpg, with a standard deviation of 2.3 mpg. Find P-Value.