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What is the least number of weightings you can use to find the counterfeit coin?

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In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?

posted Jul 17, 2014 by Vrije Mani Upadhyay

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