Problem 9 · 2023 Math Kangaroo
Medium
Spatial & Visual Reasoning
composition
Jan sticks these three pieces of paper on top of a black circle. Which picture can he not obtain?
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Answer: C
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Hint 1 of 3
Jan only owns three fixed paper shapes, so any picture he makes must be those exact shapes laid over the black circle.
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Hint 2 of 3
For each answer, try to picture placing the three pieces to leave that pattern of black showing through.
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Hint 3 of 3
Four of the pictures can be built this way; the odd one out needs a piece Jan does not have.
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Approach: test each picture against the shapes and sizes of the three covering pieces
- Jan only has one half-disc and two quarter-discs, so the grey-and-white area they create must add up to those exact sizes and shapes.
- Four of the pictures can be made by placing the half-disc and the two quarters in suitable positions.
- The remaining picture would need pieces of sizes Jan does not have, so it cannot be produced.
- That impossible picture is C.
Mark:
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