The Puzzle

Twelve coins appear identical, but one, you are told, weighs differently from the rest. Given nothing but a balance, find the odd coin in three measurements. The balance tells you which of its plates is heavier, or whether both plates have the same weight.

You don’t need to do anything tricky like using external devices, bribing the concierge with a balance and asking him to identify the coin. There is no need for right brained liberalism. Approach the problem like a typical logic problem. The puzzle is not meant to test how devious you can be.