Which of the following would you use to find the number of different combinations of six-person nominating committees that could be chosen from a class of 25 students?

To answer this question, we need to remember that in a committee is not important the order of the members. In this case, we can use combinations.
Combinations of k elements from n can be represented by the next formula:
[tex]nC_k=\frac{n!}{(n-k)!k!}[/tex]Therefore, if we have that k = 6, and n = 25. Then, we have:
[tex]25C_6=\frac{25!}{(25-6)!6!}[/tex]And since:
[tex]25C_6=\frac{25!}{(25-6)!6!}=\frac{25!}{6!(25-6)!}[/tex]In summary, therefore, the correct option is C.