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Math Help - Permutation/Combination Problem Help

  1. #1
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    Permutation/Combination Problem Help

    Hello, all.

    I got the problem

    (a) xP2

    (b)
    xC2


    The answers in the back of the book say (a)
    X2-X and (b) X2-X over 2

    I can do these problems normally, but when they threw the X in there, it confused me greatly. Anyone able to lead me in the right direction?

    --Thanks
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
    Joined
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    Santa Cruz, CA
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    Quote Originally Posted by HardyHar View Post
    Hello, all.

    I got the problem

    (a) xP2

    (b)
    xC2


    The answers in the back of the book say (a)
    X2-X and (b) X2-X over 2

    I can do these problems normally, but when they threw the X in there, it confused me greatly. Anyone able to lead me in the right direction?

    --Thanks
    The x shouldn't be much of an issue...

    _x P_2=\frac{x!}{(x-2)!}=\dots

    _x C_2=\frac{x!}{2!(x-2)!}=\dots

    Just note that x!=x(x-1)(x-2)!

    Can you take it from here??

    --Chris
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  3. #3
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    Joined
    Oct 2008
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    Quote Originally Posted by Chris L T521 View Post
    The x shouldn't be much of an issue...

    _x P_2=\frac{x!}{(x-2)!}=\dots

    _x C_2=\frac{x!}{2!(x-2)!}=\dots

    Just note that x!=x(x-1)(x-2)!

    Can you take it from here??

    --Chris
    Yes, sir. Thank you.
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