A piece of paper had the following diagram:

               o              o o o o
      From:   o o         To:  o o o
             o o o              o o
            o o o o              o

Below it, it read "Given the initial formation of ten coins, move exactly # coins to produce the end formation." It was pretty obvious that # stood for a digit, but it was smudged and couldn't be read. What possible numbers could it have been so the problem was solvable?

To allow explaining the solution, number the coins like this:

           0 
          1 2
         3 4 5
        6 7 8 9

Note: This problem was inspired by a forum question by Nicole.

Place one coin on each of the ten circles of the "From:" side of the diagram.  If the missing digit is a "0", move no coins from their position on the diagram.  Instead, rotate the paper 180 degrees and now you have the same diagram, but the coins are on the opposite side in the "To:" formation.

Posted by Mindy Rodriguez on 2005-11-22 23:33:54