The Pearls Problem
Problem: you have 12 identical pearls, except that one is a fake and has a different weight. You don't know if the defective one is lighter or heavier. You also have a scale which can only indicate if its plates are balanced (both sides weight the same) or unbalanced, in which case you see which side is heavier and which side is lighter. Identify the defective pearl by using the scale only three times.
