# The Counterfeit Coin

You have nine coins. One of the nine is counterfeit. The counterfeit coin can only be
distinguished by weight—it is slightly heavier than the rest. Using a balance scale what’s the least amount of weighings to find the counterfeit coin.

### 5 guesses to The Counterfeit Coin

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• the least amount of weight is 1/16 of a ounce

• dude

Nope, that’s not it.

We’re looking for the least amount of weighings to find the counterfeit coin.

Keep trying!

• Roolstar

2 weighings would be enough:

Just divide the nine coins in 3 groups of 3 coins each A, B & C

Weighting 1: Compare A & B
If one of them is heavier Take it to Weighing 2, if not, take C to weighing 2

Weighing 2: Compare 2 coins from that group
If one of them is heavier, you found it, if not, it’s the 3rd coin not on the scale.

• Roolstar

How many weighings are needed to find the counterfeit coin in a 27 coins group?