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The False Coin

 

You are given 18 coins but you find out that one of the coins (you don't know which) is fake and weighs less than any of the others.

 

How can you be able to detect the false coin using nothing but a normal balance scale only three times?

Posted

The False Coin

 

You are given 18 coins but you find out that one of the coins (you don't know which) is fake and weighs less than any of the others.

 

How can you be able to detect the false coin using nothing but a normal balance scale only three times?

 

 

 

1) Compare 2 stacks of 6 coins from the 18 coins

 

If set A > B, keep set A; if B > A, keep set B, if A = B, keep the 6 coins you did not weigh.

 

2) Compare 2 stacks of 2 coins from the 6 coins you kept

 

If set A > B, keep set A; if B > A, keep set B, if A = B, keep the 2 coins you did not weigh.

 

3) Compare the 2 coins you kept

 

Whichever weighs less is the false one

 

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