12 balls, equal in size and appearance. However, one weighs differently. You have an equal-arm-balance and 3 tries to figure out which one is different, heavier or lighter.
John met Dave at the bus stop. They hadn't seen each other for a long time. John to Dave: "how old are your three kids now?" Dave: "I won't tell you, but I'll give you a clue--the product of their ages is 36." John immediately said, "well, I need another clue." Dave: "the sum of their ages is equal to the number on the bus that just went by." John thought for a while and said "I need another clue." Dave: "the oldest one is a red-head." John: "now I know their ages." So, do you know their ages?