Riddle of the Week

Riddle of the Week: The Pool Ball Problem

Difficulty level: Very Hard

Michael Stillwell

By Jay Bennett

This week's riddle is one of my all-time favorites. The question is simple enough. The solution is not.

PROBLEM

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 heavier or lighter.

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 heavier or lighter, in just three weighings?