C(x,y) = number of ways to choose y elements out of x total

x!

----

y! (x-y)!

how many ways to choose 3 women out of 10 = C(10,3)

how many ways to choose 0 men out of 10 = C(10,0)

how many ways to choose 3 women out of 10 and 0 men out of 10 = C(10,3)*C(10,0)

how many ways to choose 3 people out of 20 = C(20,3)

probability will choose 3 women out of 10 and 0 men out of 10

C(10,3)*C(10,0)/C(20,3)