2007 AMC 10B Problem 3

Attempt Problem 3 of the 2007 AMC 10B below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2007 AMC 10B solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

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?

$22$

$24$

$25$

$26$

$28$

Answer: B

Concepts:harmonic mean rate

Difficulty rating: 980

Solution:

The student used $120/30=4$ gallons driving home and $120/20=6$ gallons returning, for $10$ gallons over $240$ miles.

The average is $240/10 = 24$ miles per gallon.

Thus, the correct answer is B.

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