Problem 5 · 2010 Math Kangaroo
Easy
Spatial & Visual Reasoning
spatial-reasoning
Six coins make a triangle (see the picture). What is the smallest number of coins that must be moved to make the circle?
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Answer: B — 2
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Hint 1 of 2
Picture the 6-coin ring on top of the triangle and see which coins already sit in the right spots.
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Hint 2 of 2
Count how many coins are NOT already where the ring needs them.
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Approach: keep the coins already in place, move only the rest
- Lay the target ring of 6 coins over the triangle.
- Four of the coins already sit where the ring needs them; only two are out of place.
- So the smallest number of coins to move is 2.
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