Problem 3 · 2009 Math Kangaroo
Easy
Geometry & Measurement
perimeter
The star shown is made by fitting together 12 congruent equilateral triangles. The perimeter of the star is 36 cm. What is the perimeter of the grey hexagon?
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Answer: C — 18 cm
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Hint 1 of 2
The star's outline and the hexagon's outline are both built from those equal triangle edges.
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Hint 2 of 2
Count how many equal edges form each outline.
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Approach: compare edge counts of equal-length segments
- The star's outline is made of 12 equal triangle edges, so each edge is 36/12 = 3 cm.
- The grey hexagon's perimeter is 6 of those same edges.
- Perimeter = 6 x 3 = 18 cm.
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