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Math Help - Permutations.

  1. #1
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    Permutations.

    10C2
    i know the answer is 45.
    but for some reason, i can't get THAT answer. i keep getting something else....

    anyone help me please?

    thank you in advance!
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  2. #2
    Junior Member
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    Quote Originally Posted by Big-K View Post
    10C2
    i know the answer is 45.
    but for some reason, i can't get THAT answer. i keep getting something else....

    anyone help me please?

    thank you in advance!
    10 C 2= \frac{10!}{8!2!} after dividing denomonator and numerator by 8! the following is obtained \frac{(9*10)}{(1*2)}=9*5=45
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  3. #3
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    But does this 10 C 2= have anything to do with the 2nd step?
    if it does, how?

    thank you!
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  4. #4
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    Quote Originally Posted by Big-K View Post
    But does this 10 C 2= have anything to do with the 2nd step?
    if it does, how?

    \frac{10*9*8*7*6*5*4*3*2*1}{8*7*6*5*4*3*2*1*2*1}

    thank you!
    well ,I assumed that you know this:

    10!=10*9*8*7*6*5*4*3*2*1

    8!=8*7*6*5*4*3*2*1

    and 2!=2*1

    Substituting this gives:

    \frac{10!}{8!2!} = \frac{10*9*8*7*6*5*4*3*2*1}{8*7*6*5*4*3*2*1*2*1} = \frac{9*10}{2}=45
    Last edited by mr fantastic; January 25th 2009 at 09:46 PM. Reason: Added some spacing to make it easier to read.
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