Answer
$_{10}C_3=120$
Work Step by Step
$_nC_r=\frac{n!}{r!(n-r)!}$
$n=10$ and $r=3$
$_{10}C_3=\frac{10!}{3!(10-3)!}=\frac{10!}{3!\times7!}$.
But, $10!=10\times9\times8\times(7\times6\times\times4\times3\times2\times1)=10\times9\times8\times7!$
$_{10}C_3=\frac{10\times9\times8\times7!}{3!\times7!}=\frac{10\times9\times8}{3\times2\times1}=\frac{720}{6}=120$
