Puzzle of the week: The twelve-coin problem There are twelve coins, eleven of which are identical and one of which is different, but it is not known whether it is heavier or lighter than the others. You have a traditional balance scale with two pans. To use such a scale, you place a coin into each pan and the scale will determine which coin is heavier. The balance or scale may be used three times to isolate the unique coin and determine wether it is heavier or lighter than the others.