You have ten bags of coins, one of them full of fake coins, the rest real. Each of the fake coins weighs one gram less than a real coin. But, while you have scales, you are only allowed to weigh once.
Stumped? Here is the answer.
You take one coin out of bag number one, two coins out of bag number two, three out of bag number three, and so on, until you take ten coins out of bag number ten. Then you put all those coins on the scales.
If the weight is one gram less than it should be, then the fakes are in bag number one.
If the result is two grams less, then the second bag has the counterfeits.
If the weight is ten grams less, then the tenth bag is the one that should be discarded.
Brian Easton got it right. I didn't.
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