At most how many times can you find out the lighter coin among 81coins by a balance only

Logic Level 2

There are 81 coins with identical look but one of them is slightly lighter than others.(The balance is accurate and tough enough)(no lucky situation)


The answer is 4.

God: Sun God by God: Sun God , 20, Hong Kong

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1 solution

God: Sun God
Aug 5, 2018
  • Divide 81 coins into 27,27,27.Measuring any two of them.
  • If the lighter coin hides on the balance, the balance shows the side it hides.
  • If they are balancing,the lighter coin is hiding in the rest of 27 coins.
  • When you find the 27 coins which the coins hides,do the same way to 27 coins.
  • Repeating 3 times again, you will find it.
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