1953 AMC 12 Problem 26

Attempt Problem 26 of the 1953 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 1953 AMC 12 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

26.

The base of a triangle is 1515 inches. Two lines are drawn parallel to the base, terminating in the other two sides, and dividing the triangle into three equal areas. The length of the parallel closer to the base is:
565\sqrt6 inches
1010 inches
434\sqrt3 inches
7.57.5 inches
none of these
Answer: A
Concepts:similar trianglesarea ratioparallel lines
Small hint:
The triangle above the lower parallel contains two-thirds of the total area
Big hint:
For similar triangles, the area ratio is the square of the corresponding-length ratio
Solution:
The parallel closer to the base bounds a smaller triangle above it whose area is 23\frac{2}{3} of the whole triangle. If its length is x,x, similarity gives x2152=23. \frac{x^2}{15^2}=\frac23. Hence x2=150x^2=150 and x=56.x=5\sqrt6.
Thus, the correct answer is A.
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