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Math Help - Need help finding "n" in Permutations!

  1. #1
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    Need help finding "n" in Permutations!

    Link 1: http://i42.tinypic.com/zu2fwj.png
    Link 2: http://i40.tinypic.com/e8rhvs.png

    Please help me. I do not know how to solve for n. Thank you.
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  2. #2
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    Quote Originally Posted by krzyrice View Post
    Link 1: http://i42.tinypic.com/zu2fwj.png
    Link 2: http://i40.tinypic.com/e8rhvs.png

    Please help me. I do not know how to solve for n. Thank you.
    Link1: ^nP_8 = 13 \cdot ^nP_7.

    Substitute the definition ^nP_r and simplify. Then solve the resulting simple linear equation for n. Note that (n - 7)! = (n - 7)(n - 8)!


    Link2: ^nP_6 = 90 \cdot ^nP_4.

    Done in a similar way. Yiou will end up with a quadratic equation to solve. Note that one of the solutions to this quadratic equation is not be valid.
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  3. #3
    Member SengNee's Avatar
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    Quote Originally Posted by krzyrice View Post
    Link 1: http://i42.tinypic.com/zu2fwj.png
    Link 2: http://i40.tinypic.com/e8rhvs.png

    Please help me. I do not know how to solve for n. Thank you.
    Link1:

    nP8=13 \bullet nP7
    n(n-1)(n-2)(n-3)(n-4)(n-5)(n-6)(n-7)=13n(n-1)(n-2)(n-3)(n-4)(n-5)(n-6)
    n-7=13
    n=

    Link2:
    Use the same concept but remember n should be greater than 6.
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  4. #4
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    thank you so much for the help guys
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