Answer
$35$
Work Step by Step
The number of arrangement of choosing $r$ objects out of $n$ distinct object $(r \leq n)$ is:
$(a)$ If order matters, use permutation, i.e, $P(n, r)$.
$(b)$ If order doesn't matter, use combination, i.e, $C(n, r)$.
Order doesn't matter since once 4 students are chosen for the committee, no matter how you arrange them, they are still same 4 students.
Therefore, $C(7, 4) = \frac{P(7, 4)}{4!} = \frac{840}{24} = 35$
