Counterfeit Coins

The Counterfeit Coins - Martin Gardner - Best Mathematical and Logical Puzzles

"You have 10 stacks of coins, each consisting of 10 coins. One entire stack is counterfeit, but you do not know which one. You do know the weight of a genuine coin and you are also told that each counterfeit coin weighs 1 gram more than it should. You may weigh the coins on a pointer scale. What is the smallest number of weighings necessary to determine which stack is counterfeit ?"
- Martin Gardiner, Counterfeit Coins Puzzle.

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