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Math Help - Permutation or combination?

  1. #1
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    Permutation or combination?

    Nine students enter a classroom with 15 desks. How many seating arrangements are possible if each student selects a desk?

    p = n!/(n-r)! = 165110400 doesn't sound right

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  2. #2
    Senior Member yeKciM's Avatar
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    Quote Originally Posted by terminator View Post
    Nine students enter a classroom with 15 desks. How many seating arrangements are possible if each student selects a desk?

    p = n!/(n-r)! = 165110400 doesn't sound right

    Thanks
     \displaystyle \frac {n!}{k!(n-k)!}
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  3. #3
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    Quote Originally Posted by terminator View Post
    Nine students enter a classroom with 15 desks. How many seating arrangements are possible if each student selects a desk?
    p = n!/(n-r)! = 165110400 doesn't sound right
    I have no idea how you got that answer. BUT
    P(15,9)=\dfrac{15!}{6!}=1816214400
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  4. #4
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    The other member said is a combination.
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  5. #5
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    The other member said is a combination(at least the first formula)
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  6. #6
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    In any normal classroom the seats are different: perhaps numbered.
    The students are clearly distinct.
    So this is a permutation of 15 taken 9 at a time.
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  7. #7
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    Thumbs up thanks

    always prompt and ready to help.
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