There are 10 coins forming an equilateral triangle: 4 at the base, 3 on top, then 2 and 1 on top. Moving only three coins, reverse the triangle so that it points downward.
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The triangle of coins
Good movement puzzles don't ask for strength, but for symmetry. Here the final drawing is already hinted at in the initial one; The difficulty is to see which three coins carry all the transformation.
Hints
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- Don't try to disassemble the entire figure: look for how much the inverted triangle can overlap with the original.
- If you mentally place the final triangle, you will see that most of the coins can stay still.
- The three coins that move are the one at the top and the two at the ends of the base.
Solution
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Answer: Yes: just move three coins. Explanation: The key is not to rebuild the triangle from scratch, but to make the inverted triangle share as many coins as possible with the initial one. If you mentally slide an identical triangle pointing downwards over the original figure, you will see that 7 coins can stay where they are and only 3 need to be relocated. Which ones move? Exactly the three that are outside of that overlap: - the top tip coin,
- and the two coins at the ends of the base. These three go on to occupy the three missing positions in the inverted triangle: - one goes to the bottom tip,
- and the other two at the upper ends of the new figure. Thus the triangle is inverted with only three movements.
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