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2018 Math Kangaroo

Problem 6

Problem 6 · 2018 Math Kangaroo Hard
Geometry & Measurement area-decompositionarea-fraction

In the three regular hexagons shown, X, Y and Z are (in this order) the areas of the grey shaded parts. Which statement is true?

Figure for Math Kangaroo 2018 Problem 6
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Answer: A — \(X=Y=Z\)
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Hint 1 of 2
Split each hexagon into six identical small triangles.
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Hint 2 of 2
Count how many of those six equal triangles are shaded in each hexagon.
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Approach: measure each shaded region in sixths of the hexagon
  1. A regular hexagon divides into six congruent equilateral triangles.
  2. In each of the three pictures the grey region covers exactly three of those six triangles, i.e. half the hexagon.
  3. Since the hexagons are the same size, X, Y and Z are all equal.
  4. So \(X=Y=Z\).
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