6.02: Nine Balls. You have nine balls. Eight are of the same weight, and one is heavier. You are given a balance which tells you only whether the left side or the right side is heavier. Find the heavy ball in just two uses of the scale.
Weight 2 groups of 3. Set 1 group of 3 off to the side. Deduce heaviest group from first scaling. Weight last group of 3, weight 2 balls, set one off to the side. Deduce heaviest group.