This is an example from the book... howd they get to 20*10!?!
From a pool of six women, Tanya must "choose" (hint, hint) three to start the game. And from five men, she must "choose" two. So, how many combinations can be formed on six items, taken three at a time? If your answer is "6 choose 3", i.e., 6c3, then you are correct. Similarly, there are 5c2 ways of selecting two from five. Hence, by the product rule, the number of ways by which Tanya can choose the five starting players is (6c3)*(5c2) = (6*5*4 /3!)(5*4 /2!) = 20(10).
I hope that answers it fror you.