12 Marbles
You have twelve marbles, all exactly identical in shape, color, texture, etc
except for one which is slightly different in weight. You also have a two-sided
scale. What is the minimum number of weighs to guarantee you know which marble is
the odd one?
Part 1: You know that the odd one out is heavier than the others.
Part 2: You don't know if it's heavier or lighter than the others.