Riddle of the Week

Riddle of the Week: Heads or Tails?

Difficulty level: Moderate

By Jay Bennett

This might throw you for a loop at first, but once you know it, the answer seems beautifully simple. Mull it over for a while and you won't regret it.

PROBLEM

You sit at a sprawling table with hundreds of thousands of quarters in front of you, but you don't know exactly how many. You have a blindfold on, so you cannot see the quarters, but you do know that exactly 20 quarters are tails-side-up, and the rest are heads-up.

You can move the quarters and flip them over as much as you want—but remember, you cannot see what you are doing. Though you can feel the quarters, you cannot determine which side is heads and which side is tails just by touch.

How do you separate the quarters into two piles that have the same number of tails-side-up quarters in them?

HINT

The total number of quarters in each pile is irrelevant.