This is a classic. Forgive me if this has been posted before. You have 12 coins, and you know that one one of the coins may be fake. You also know that a fake coin will not have the same weight as a good coin: it will either be heavier or lighter. You have at your disposal a balance scale. This scale will only tell you if the weight of the items in the left side are heavier, lighter, or equal to the weight items in the right side. Devise a method to determine which coin (if any) is bad and if the bad coin is heavy or light using only three scale measurements.