Problem 14 · 2010 Math Kangaroo
Stretch
Geometry & Measurement
areagrid-counting
The big equilateral triangle consists of 36 small equilateral triangles which each have 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 big triangle has area 36; work out ABC as a fraction of it.
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Hint 2 of 2
Slice ABC along the grid lines into small triangles and count them.
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Approach: count unit triangles inside ABC
- The big triangle splits into 36 unit triangles, total area 36 cm².
- Reading the grid, triangle ABC covers the equivalent of 11 of those unit triangles.
- So the area of ABC is 11 cm².
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