Answer
21
Work Step by Step
We know the following equation for combinations:
$$nC_r = \frac{n!}{(n-r)!\cdot r!}$$
Thus, we find:
$$\frac{7!}{2!\left(7-2\right)!}\\ 21$$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.