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Puzzle 21) The Odd Coin

Submitted by Abhishek Jain, on August 24, 2017

Puzzle

You have 12 gold coins of same weight except one, which weighs less than others. You are given a balance machine but no weighing measures. You can use the balance machine three times only. The balance machine tells you just which side weighs more. How can you find the odd coin just by weighing the available coins?


Important points of puzzle (Key points):

  1. There are 12 gold coins, 11 of same weight and one with less weight than others.
  2. You have a balance machine which indicates towards the side weighs more.
  3. You have no weighing measures.
  4. Constraint: You can use the balance machine three times only.
  5. Task: How can you find the odd coin?

Answer

Firstly, weigh 6 and 6 coins in two batches. From the batch that weighs less, weigh 3 and 3 again. From the batch that again shows less weight, take two coins and weigh them to know which is of less weight. You would know the answer. If both are equal, then the third coin is the odd one.


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