Problem 9 · 2021 Math Kangaroo
Easy
Spatial & Visual Reasoning
foldingsymmetry
Mary had a piece of paper. She folded it exactly in half. Then she folded it exactly in half again. She got the small shape shown on the left (a right triangle). Which of the shapes P, Q or R could have been the shape of her original piece of paper?
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Answer: E — any of P, Q or R
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Hint 1 of 2
Folding once then again maps the original onto a quarter-size shape; run it backwards.
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Hint 2 of 2
Unfold the right triangle twice and check which of P, Q, R it could grow back into.
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Approach: unfold the result twice
- Folding a sheet in half twice can turn a rectangle, a square, or a larger right triangle into this small right triangle.
- Unfolding the given triangle can recreate any of shapes P, Q or R, so the answer is E (any of P, Q or R).
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