Problem 85 from http://mathproblems.info/group5.html

In front of you are 12 pearls, 11 being real and one fake. The real ones all weigh the same and the fake one differs in weight from the real ones (may weigh more or less). With a balance scale and three weighings how can you weed out the fake one and determine whether it is too heavy or too light?

The problem states that the counterfeit can be heavier or lighter than the others, but the second case of your solution presupposes that it is lighter. How can you tell whether it is heavier or lighter?