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There are 100 piles of coins in a warehouse, each coin is supposed to have a mass of one gram. However, one of the piles is counterfeit. It’s coins have a mass of 3/4 of a gram. How can you find the counterfeit pile by using an electric scale one and only once?
May 14th, 2011
label the piles from 1 to 100. take coin(s) as indicated on their labels (a coin from pile 1, 2 coins from pile 2, and so on) and put all of them together on the scale. find the difference of weight the pile is with the weight it usually does if theres no counterfeit. time by 4(or actually divide by 1/4). there’s ur answer(the pile labelled with that number)
u should have 100(1+100)/2=5050 coins in the pile u weight.
the “un”counterfeit weight=5050 grams.
I was thinking along the same lines as the first answerer. My way is that you put all the piles on the scale, and remove them one by one. Whichever one reduces the reading by 3/4 gram is the counterfeit.