# There are nine identical- looking coins. One of the coins is counterfiet and weighs less than the other coins.

The only scale available is a balance scale, on which you can weigh any number of coins against each other. Using the scale only twice, figure out a way to find the counterfeit coin.

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divide the coins into groups of three and compare the masses of two groups; if one trio is heavier, simply compare two coins from that one and you’re done.

On the other hand, if the two triplets you weighed out have the same mass, compare two coins from the trio you initially left out

Three piles of three coins each. Place two of these piles on the balance. If equal, the third pile has the counterfeit coin. If one is lighter than the other it is the pile that has the counterfeit. (1st use of balance)

Take the pile that has the counterfeit. Place one coin on each side of the balance. If one is lighter, it is the counterfeit. If they are both equal in weight, the third coin is counterfeit. (2nd use of balance)