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2024 Math Kangaroo

Problem 12

Problem 12 · 2024 Math Kangaroo Hard
Logic & Word Problems careful-countingcasework

Anna, Bella, Che and Dimitry each have three shapes. Each child shares exactly one of their shapes with one other child. Anna has a triangle, a circle and a square; Bella has a heart, a square and a star; Che has a star, a triangle and a diamond. Which three shapes does Dimitry have?

Figure for Math Kangaroo 2024 Problem 12
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Answer: E
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Hint 1 of 3
Write out the shapes the other three children have and see which ones already come in matching pairs.
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Hint 2 of 3
Some shapes already appear for two children (a pair), but a few shapes appear for only one child so far.
Still stuck? Show hint 3 →
Hint 3 of 3
Dimitry must hold exactly the shapes that still need a partner, so that every shape ends up shared by two children.
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Approach: give Dimitry the shapes that still need a matching partner
  1. Among Anna, Bella and Che, the square (Anna & Bella), the star (Bella & Che) and the triangle (Anna & Che) already come in pairs.
  2. That leaves the circle (only Anna), the heart (only Bella) and the diamond (only Che) without a partner.
  3. So Dimitry must have the circle, the heart and the diamond — this pairs every shape with exactly one other child, which is option E.
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