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Math Help - Combination - KEY QUESTION

  1. #1
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    Combination - KEY QUESTION

    Solve for n if P(n,3) = 2C (n,2)
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  2. #2
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    Quote Originally Posted by cnmath16 View Post
    Solve for n if P(n,3) = 2C (n,2)
    P(n, 3) = 2 C(n, 2)

    \frac{n!}{(n-3)!}=2\frac{n!}{(n-2)! \;2!}

    n(n-1)(n-2)=2\frac{n(n-1)}{2\times 1}

    n(n-1)(n-2)-n(n-1)=0

    n(n-1)[(n-2)-1]=0

    n(n-1)(n-3)=0

    n=0, 1, 3

    since, in P(n, r), n\ge r

    therefore, n\ge 3

    so, n = 3

    did you get it now???
    Last edited by Shyam; November 23rd 2008 at 04:10 PM.
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