2003 AMC 10A Problem 4

Below is the professionally curated solution for Problem 4 of the 2003 AMC 10A, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2003 AMC 10A solutions, or check the answer key.

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Concepts:distance rate and time harmonic mean

Difficulty rating: 1130

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?

$3$

$3.125$

$3.5$

$4$

$4.5$

Solution:

Mary walks a total of $2$ km in $30 + 10 = 40$ minutes.

Since $40$ minutes is $\dfrac{2}{3}$ hour, her average speed is $2 \div \dfrac{2}{3} = 3$ km/hr.

Thus, the correct answer is A.

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