Answer
$126$
Work Step by Step
Combinations Rule
$$\binom{N}{n} = \dfrac{N!}{n! (N-n)!}$$
${\displaystyle{\binom{9}{4}} = \dfrac{9!}{4! \, 5!}= \dfrac{9 \cdot 8 \cdot 7 \cdot 6 \cdot 5 \cdot 4 \cdot 3 \cdot 2 \cdot 1}{(4 \cdot 3 \cdot 2 \cdot 1)(5 \cdot 4 \cdot 3 \cdot 2 \cdot 1)}}= \dfrac{9 \cdot 8 \cdot 7 \cdot 6}{4 \cdot 3 \cdot 2 \cdot 1}$
${\displaystyle{\binom{9}{4}} = \dfrac{9 \cdot 8 \cdot 7 \cdot 6}{4 \cdot 3 \cdot 2 \cdot 1}} = \dfrac{3024}{24} = \boxed{126}$
