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Math Help - Combinations or Perms

  1. #1
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    Combinations or Perms

    If I have a set of 6 elements {a,a,a,b,b,b} and I want to find the number of ways to arrange these in different orders, is it perms or combs that I use?
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  2. #2
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    Quote Originally Posted by dave1022 View Post
    If I have a set of 6 elements {a,a,a,b,b,b} and I want to find the number of ways to arrange these in different orders, is it perms or combs that I use?
    Strictly speaking it is neither. It is arrangements with repetitions.
    Say the problem was the same instructions but with \{a,a,b,b,b,c,c,c,c\} .
    Then the answer would be  \frac{9!}{2!\cdot 3! \cdot 4!}.
    We divide to account for the repetitions.

    What is the answer to your original question?
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  3. #3
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    Surely if I only have two discrete elements recurring a number of times it's just total!/a!*b! which is just totalC(a or b)
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    Quote Originally Posted by dave1022 View Post
    Surely if I only have two discrete elements recurring a number of times it's just total!/a!*b! which is just totalC(a or b)
    Yes. But don't you want to know the general solution?
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