2007 AMC 10B Problem 3

Question

A college student drove his compact car

120

miles home for the weekend and averaged

30

miles per gallon. On the return trip the student drove his parents’ SUV and averaged only

20

miles per gallon. What was the average gas mileage, in miles per gallon, for the round trip?

22

24

25

26

28

Average mileage is total distance divided by total gallons, not the average of the two rates

Find the gallons used each way, then divide

240

by their sum

The student used

\frac{120}{30}=4

gallons driving home and

\frac{120}{20}=6

gallons returning, for

10

gallons over

240

miles.

The average is

\frac{240}{10} = 24

miles per gallon.

Thus, the correct answer is B.

Problem 3 in other years