Problem Solving

swerve wrote:A certain car uses 12 gallons of gasoline in traveling 240 miles. In order for the car to travel the same distance using 10 gallons of gasoline, by how many miles per gallon must the car's gas mileage be increased?

A. 2
B. 4
C. 6
D. 8
E. 10

The OA is B

Source: GMAT Paper Tests

We are given that a certain car uses 12 gallons of gasoline in traveling 240 miles.

Since rate = distance/gallons used, the rate of the car, in miles per gallon, is 240/12 = 20 mpg.
If the car were to travel the same distance using 10 gallons of gasoline, the rate, in miles per gallon, would be 240/10 = 24.

Thus, the new rate is 4 mpg more than that of the old rate.

Answer: B