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.