1. Twenty-five girls are bored.. How many ways may the girls form two teams of 5 to play basketball against each other?

- This I used C(25,5) * C(20,5) and got 823,727,520. The answer in the back says it is 411,863,760. It might just be coincidence but the answer in the back is half the number I got.

2. A fraternity consisting of 30 members wants to play 7 vs. 7 flag football. How many different match-ups are possible?

-This I used C(30,7) * C(23,7) and got 4.99x10^11. The answer in the back says 2.495x10^11. Again, half my answer.