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Suppose there are 100 coins that are arranged into 10 piles of coins each pile consist of 10 coins. There is exactly one pile where all the coins are fake and all coins on the other pile are genuine. Assuming that the weight of the fake coin is different from a genuine one, what is the minimal number of weighing to determine which pile is the fake one (say here you have a digital weighing machine ).

Question

anonymous · Answer

i think 3

anonymous · Answer

has to be 3
let the weight of the fake pile be x and the real pile be y
if he finds y and x, he won't know which is fake so he needs one more y to confirm that x  is fake and not y

watchmath · Answer

Remember this is a digital weighing machine. How you can make sure that your method of weighing can determine the fake pile?