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

1. ## Why is (15 over 4) = to (15 over 11)

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

Not division

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

If you're not using "over" to represent division, then what ARE you using it for?

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

It just has in parenthesis 15 over a 4 without a line between them.

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

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

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

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

It's on my homework...teacher hasn't taught it to us yet.

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

Originally Posted by IStandAlone99
It just has in parenthesis 15 over a 4 without a line between them.
You are clearly about binomial coefficients.

$\dbinom{N}{k}=\dfrac{N!}{k!(N-k)!}$ so show that $\dbinom{15}{4}=\dbinom{15}{11}~.$