Problem 17 · 2020 Math Kangaroo
Hard
Spatial & Visual Reasoning
sequence-of-figures
Which of the following rigid wire pieces, when duplicated, lets you make a closed shape without crossings, joining the two copies at their ends?
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Answer: B
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Hint 1 of 2
Two copies of the same piece are joined end-to-end to form a single closed loop with no crossings.
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Hint 2 of 2
A piece works if its shape plus a half-turn copy of itself wraps into a closed, non-crossing curve.
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Approach: join a piece with a rotated copy of itself into a loop
- You copy the wire and connect the two copies at their ends to make one closed loop without crossings.
- This works only when a piece together with a half-turn copy of itself closes up neatly.
- Testing the shapes, piece B joins into a clean closed loop.
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