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Math Logic problem

  1. May 4, 2009 #1
    1. The problem statement, all variables and given/known data

    I am supposed to prove that if you have a puzzle 8 in this configuration

    A B C
    D E F
    H G

    I have to prove that no matter how many moves you make (as you
    would a normal puzzle moving one of the adjacent letters into the
    blank space) you cannot make the configuration

    A B C
    D E F
    G H

    I know you can't. I have moved these letters around all over the place... but how do I start to prove it... I don't know where to start



    2. Relevant equations



    3. The attempt at a solution

    I just want a starting point...
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. May 4, 2009 #2

    Mark44

    Staff: Mentor

    This is an interesting problem.

    Isn't the idea that you can slide a letter left or right, or up or down into an empty spot? The physical puzzles I've seen like this won't let you slide a letter diagonally.

    I don't know for sure, but I think that what you need to do here is to look at all the ways the blank can move around, starting from the "home" position, and getting back to it.

    For starters, the blank could move all around the 2x2 square at the lower right. At each of the four positions what is state of the puzzle.
    It could move around the two rightmost columns. At each of the six positions, what is the state of the puzzle?
    It could move all around the two lower rows. At each of the six positions, what is the state of the puzzle?
    It could move all around the perimeter of the puzzle. At each of the eight positions, what is the state of the puzzle?
    I can't think of any other possibilities, although there might be some I haven't counted.

    Once you exhaust the possible moves, and the one you're looking for doesn't appear, that would convince me that it's not possible. You have to make sure that you haven't omitted any possible puzzle states, though.
     
  4. May 4, 2009 #3

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    The proof of impossibility for games like this involves assigning a even or odd number to each game position and then showing that a move in the game can only change that number by two. So if the starting position is even and the final position is odd, you can't get from one to the other. This is a simple version of the '15 puzzle' - you can look that up for details.
     
  5. May 4, 2009 #4
    how do I look it up? Sorry new at this
     
  6. May 4, 2009 #5
    use google
     
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