The Hundred Coins Puzzle

You have 100 coins lying flat on a table, each with a head side and a tail side. 10 of them are heads up, 90 are tails up. You cannot feel, see, or in any other way find out which side is up. Split the coins into two piles such that there are the same number of heads in each pile.

Answer: Split the coins into a pile of 90 and a pile of 10. Then flip all …