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Math Help - Combinatorics

  1. #1
    Member elninio's Avatar
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    Combinatorics

    I'm stumped on this recreational problem:

    How many 5-digit numbers are there such that every next digit is smaller than the previous one?
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  2. #2
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    Quote Originally Posted by elninio View Post
    I'm stumped on this recreational problem:

    How many 5-digit numbers are there such that every next digit is smaller than the previous one?
    \binom{10}{5}
    Last edited by Plato; September 30th 2009 at 08:32 AM.
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  3. #3
    Member elninio's Avatar
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    Hmm, I didnt think it would be that simple!
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    Quote Originally Posted by elninio View Post
    Hmm, I didnt think it would be that simple!
    Well give me any subset of five digits.
    Say \{3,9,0,7,4\}.
    Arrange is desending order: 97430.
    That's sort of number described.
    So it is just the number of five element subsets of the digits.
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