So

(n!/X!(n-X)!) (p^X(1-p)^n-x)

Or would another probability method be preferred?

The question is below

It is found that 30% of Americans who exercise daily by running are men. A randomly selected group comprises of 20 people who exercise daily, with a certain number of men in the group. What is the approximate probability that there will be an exactly 15 males in the group?