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.

(In reply to re: 7 ways - your rules by brianjn)

Good point. Can we start rolling coins, say starting with 6, to form the "to" shape off of the 9? In this case, the 6 would end to the right of 9 and would be the left most corner of the "to" shape. We should peel the coins off and on to avoid the trapped coin/space issue, and finish with the 9 rolling to the last new spot. How does this sound?

Posted by owl on 2005-08-15 15:23:34