# counterfiet coin puzzle?

there are ten stacks of ten silver dollars. you are given the weight of a real silver dollar, and are told each counterfeit coin weighs one gram more than a real silver dollar. you also know that one of the stacks is completely counterfiet, and you can use a scale that weighs by grams, what is the minimum number of weighings needed to determine the counterfeit stack?

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Hello,

Take 1 coin from the first stack, 2 coins from the second stack, 3 coins from the third stack and so on until you have taken 10 coins from the last stack. Now you have 55 coins

( 1+2+3+4+5+6+7+8+9+10) = 55. However much 1 coin weighss (letâ€™s say it weighs 2 grams) you should have 2 * 55 or 110 grams, but since one stack is counterfeit you will have these weighing 1 gram apiece more than the good ones. So if the weight is one gram heavy the first pile is counterfeit, if it is two grams heavy the the second pile is counterfeit etc.

So in answer to your question: one is the minimum number of weighings that is (are) need to determine the counterfeit pile.

Hope This Helps!!

the real question is the profit margin of counterfeiting silver dollars.