Flipping 3-Coin Triangles

There are 10 coins, 5 of which are heads up and the other 5 are tails up.

On each turn, you choose exactly 3 coins in a triangle, where each coin touches the other two, and flip them over.

What is the minimum number of turns needed to make all of the coins heads up?


This problem was inspired by a previous Problem of the Week.

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