You have 12 cue balls that look and feel identical. However, one of the cue balls is either slightly lighter or slightly heavier than the rest. You cannot tell which ball is the odd one out by handling them, and you do not know if that ball is lighter or heavier. You have a set of old-fashioned balance scales. The scale with more weight in it will tip down, and the scale with less weight in it will tip up. How do you figure out which ball is the odd one out, and whether it is lighter or heavier, in just three weighings?
