20 women and 10 men is 30 people. Since there are no restrictions on the gender composition of the groups of three, you can simply consider the group of 30 people.
You need to calculate the number of combinations of 30 things taken 3 at a time. is the number of combinations of things taken at a time and is calculated by
You can do your own arithmetic.
John
My calculator said it, I believe it, that settles it