SAT Math problem In a volleyball league with 4 teams, each team plays exactly 2 games with each other 3 teams in the league. What is the total number of games played in this league? 
the book says the answer is 12, i wondered how come is that?

Team A can play 3 games with each of the three teams.
Team B can play 3 games too , but it's game with Team A has already been counted so we leave that out. So we count 2 games.
Team C can play 3 games too , but it's game with Team A and B has already been counted so we leave those out.So we count 1 game.
Team D can play 3 games too , but it's game with Team A and B and C has already been counted so we leave those out.So we count none.
So total games =3*2*1=6
If they play two games with each other then total games is 6*2=12 .
You can count these things faster after learning Permutation and Combination.
