A merchant has a bag of 8 identical-looking gold coins, but one is counterfeit and weighs slightly less than the others. Using a balance scale with no weights, what is the minimum number of weighings required to guarantee finding the counterfeit coin?
Two weighings.
Divide the 8 coins into groups of 3, 3, and 2. Weigh two groups of 3. If they balance, weigh the remaining 2. If one group is lighter, weigh two coins from that group to find the lighter one.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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