<s>[INST] A bag contains $4$ red and $6$ white marbles. How many ways can $5$ marbles be selected if exactly $2$ must be red? 
A bag contains $4$ red and $6$ white marbles. How many ways can $5$ marbles be selected if exactly $2$ must be red?

Is it $120$?
 [/INST] We choose $2$ marbles from the $4$ red ones. For each of these $\binom{4}{2}$ choices, there are $\binom{6}{3}$ ways to choose the three white marbles. So you are correct:
$$\binom{4}{2}\binom{6}{3}=6 \cdot 20 = \boxed{120}$$
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