Problem 22 · 2010 Math Kangaroo
Stretch
Geometry & Measurement
area-decompositiongrid
The big equilateral triangle consists of 36 small equilateral triangles, each with an area of 1 cm². Determine the area of ABC.
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Answer: A — 11 cm²
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Hint 1 of 2
The whole triangle is 36 little ones, so each small triangle counts as 1.
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Hint 2 of 2
Find ABC's area by subtracting the corner regions from the whole.
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Approach: subtract corner pieces from the whole
- The big triangle has area 36 (thirty-six unit triangles).
- Removing the three corner regions around triangle ABC leaves its area.
- Triangle ABC has area 11 cm².
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