Answer
$21$
Work Step by Step
Formula to calculate the Binomial Coefficient is:
$\displaystyle \binom{n}{k}=\dfrac{n!}{k!(n-k)!}$
Let's see how this formula works:
$\displaystyle \binom{7}{2}=\dfrac{7!}{2!(7-2)!}=\dfrac{ 7 \cdot 6 \cdot 5!}{ 2 \cdot 1 \times 5!}=21$