How many combinations to make a sum?

  1. Hi all,
    Saw this problem and was wondering if there was a simpler way to do this besides listing out the possible combinations.

    In a game, each token has one possible value: 1, 5, or 10. How many different combinations of these tokens will give us a total sum of 17?
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,311
    Science Advisor
    Homework Helper
    Gold Member

    You need to rewrite the question mathematically then see if you can rework it into something that looks solvable. i.e.

    Find all points (x,y,z) which satisfy 10x+5y+z=17 - where x,y,z are integers greater than or equal to zero.

    The equation is of a plane... so the question is looking for the number of integer points in the plane that is in the positive octant.

    It is usually easier to just list and count.
    You can use your knowledge of arithmetic to find shortcuts though.
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