1959 AMC 12 Problem 30

Attempt Problem 30 of the 1959 AMC 12 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 1959 AMC 12 solutions, or check the answer key.

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30.

AA can run around a circular track in 4040 seconds. B,B, running in the opposite direction, meets AA every 1515 seconds. What is BB’s time to run around the track, expressed in seconds?

121212\dfrac12

2424

2525

271227\dfrac12

5555

Answer: B
Concepts:relative speedrate
Difficulty rating: 1140
Small Hint:

Measure each runner’s speed in laps per second

Big Hint:

Because they run in opposite directions, their speeds add to 115\frac{1}{15} lap per second

Solution:

If BB’s lap time is t,t, their relative speed is 140+1t=115. \frac1{40}+\frac1t=\frac1{15}. Thus 1t=124,\frac{1}{t}=\frac{1}{24}, so t=24t=24 seconds.

Therefore, the correct answer is B.

← Problem 29#29
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