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Math Help - Permutations.. a quick question

  1. #1
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    Permutations.. a quick question

    How exactly do i go about solving these questions:an example would be fine
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  2. #2
    TD!
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    Example: <br />
\frac{{n!}}{{\left( {n - 1} \right)!}} = \frac{{n\left( {n - 1} \right)!}}{{\left( {n - 1} \right)!}} = n<br />
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  3. #3
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    you dont have to use one of my questions but can u do an example with numbers? id understand more
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  4. #4
    TD!
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    Just replace n by a number to see an example, e.g. n = 5:

    \frac{{5!}}{{4!}} = \frac{{5 \cdot 4!}}{{4!}} = 5
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  5. #5
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    thanks... im having trouble with this one too.. funny how i get all the hard questions but not these anyways no solving needed here just an example will do( my book sucks)
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  6. #6
    TD!
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    The first one is exactly 5!, no?

    Let's take a look at the second one. It starts like 8!, but that is 8*7*6*5*4*3*2*1. But the last part 5*4*3*2*1 isn't there, and that's exactly 5!. So we need 8!, but not the 5!, so 8!/5!. Check:

    <br />
\frac{{8!}}{{5!}} = \frac{{8 \cdot 7 \cdot 6 \cdot 5!}}{{5!}} = 8 \cdot 7 \cdot 6<br />
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  7. #7
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    so say it was 30*29 whats the answer?
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  8. #8
    TD!
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    Try the same approach as above.
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