2007 AMC 10B Problem 3

Below is the professionally curated solution for Problem 3 of the 2007 AMC 10B, 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.

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Concepts:harmonic mean rate

Difficulty rating: 980

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?

$22$

$24$

$25$

$26$

$28$

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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