Why is (15 over 4) = (15 over 11)

Not division

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- May 9th 2014, 05:15 PM #1

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- May 9th 2014, 05:20 PM #2

- May 9th 2014, 05:21 PM #3

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- May 9th 2014, 05:31 PM #4

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## Re: Why is (15 over 4) = to (15 over 11)

$\displaystyle \left(\begin{array}{c} a \\ b \end{array}\right)$ is the "binomial coefficient. It is defined as $\displaystyle \left(\begin{array}{c}a \\ b \end{array}\right)= \frac{a!}{b!(a- b)!}$. So $\displaystyle \left(\begin{array}{c} 15 \\ 4\end{array}\right)= \frac{15!}{4! 11!}$ and $\displaystyle \left(\begin{array}{c} 15 \\ 11\end{array}\right)= \frac{15!}{11!4!}$. They are the same because 11+ 4= 15.

(If you really have no idea what the**notation**means, where did you see this problem?)

- May 9th 2014, 05:33 PM #5

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- May 9th 2014, 05:35 PM #6