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 by Nosher)

Yeah, you're probably right with it being a digit. Seeing as no rules were imposed I thought it would count as a valid solution to just move all 10 coins to somewhere else.

i imposed the rule that you couldn't swap any coins as it seemed like cheating if you could just move one coin and replace it with another as that is adding an extra move that is unneccessary. 

Posted by Lisa on 2005-08-16 09:49:31