2002 AMC 12A Problem 8

Attempt Problem 8 of the 2002 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 2002 AMC 12A solutions, or check the answer key.

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

8.

Betsy designed a flag using blue triangles, small white squares, and a red center square, as shown. Let BB be the total area of the blue triangles, WW the total area of the white squares, and RR the area of the red square. Which of the following is correct?
B=WB = W
W=RW = R
B=RB = R
3B=2R3B = 2R
2R=W2R = W
Answer: A
Concepts:area decompositioncongruence (geometry)
Small hint:
Cover the whole flag with congruent triangles
Big hint:
Count how many of those triangles lie in the blue region and in the white region
Solution:
Drawing the diagonals shown, the entire flag is tiled by congruent triangles. Counting, there are 2424 triangles in the blue region, 2424 in the white region, and 1616 in the red square.
Since the blue and white regions contain the same number of triangles, B=W.B = W.
Thus, the correct answer is A.
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