2003 AMC 12A Problem 4

Attempt Problem 4 of the 2003 AMC 12A 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 2003 AMC 12A solutions, or check the answer key.

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It takes Mary $30$ minutes to walk uphill $1$ km from her home to school, but it takes her only $10$ minutes to walk from school to home along the same route. What is her average speed, in km/hr, for the round trip?

$3$

$3.125$

$3.5$

$4$

$4.5$

Answer: A

Concepts:distance rate and time unit conversion harmonic mean

Difficulty rating: 1130

Solution:

Mary walks a total of $2$ km in $30+10=40$ minutes, which is $\dfrac23$ hour.

Her average speed is $2 \div \dfrac23 = 3$ km/hr.

Thus, the correct answer is A.

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