1972 AMC 12 Problem 15
Attempt Problem 15 of the 1972 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 1972 AMC 12 solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
15.
A contractor estimated that one of his two bricklayers would take hours to build a certain wall and the other hours. However, he knew from experience that when they worked together, their combined output fell by bricks per hour. Being in a hurry, he put both men on the job and found that it took exactly hours to build the wall. The number of bricks in the wall was:
Answer: C
Small Hint:
Let be the number of bricks in the wall
Big Hint:
Their actual combined hourly rate is
Solution:
If the wall contains bricks, the individual rates are and Thus Multiplying by and simplifying gives hence
Therefore, the correct answer is C.
Problem 15 in Other Years
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