You have eight coins which look identical. One of them is fake, made of a slightly heavier metal than the others. The difference in weight is too small to feel by hand, but you have a precision scale which can weigh one object (or set of objects) against another.
If you are only allowed to use the scale twice, can you pick out the fake coin from the real ones?
Bonus question: You have twelve coins which look identical. One of them is fake, and has a slightly different weight than the others. You do not know whether it will be heavier or lighter, and you cannot feel the difference by hand. Can you pick out the fake coin if you are only allowed to use the scale three times?
See the solution
Wednesday, August 5, 2009
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