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Combinatorics problem

  1. May 18, 2013 #1
    1. The problem statement, all variables and given/known data
    Let X be a set containing all four digit numbers made up of {1,2,3}, where every number contains every digit at lease once. Number of all subsets is:

    3. The attempt at a solution

    So firs i have to find number of elements in the set:

    3!*3 + 3*12 = 54

    Now what they mean by subsets? And did i calculated number of elements correctly?
     
  2. jcsd
  3. May 19, 2013 #2

    haruspex

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    54 seems too many. Pls explain your calculation.
    For the second part, if there are N elements in a set, how many subsets does it have?
     
  4. May 19, 2013 #3

    Simon Bridge

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    It could be they want to know how many possible subsets of X there are.
    i.e. any member of X would be a subset of X of size 1. any pair of members would be a subset size 2, etc.
    [haruspex beat me :)]
     
    Last edited: May 19, 2013
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