There are 5 girls and 5 boys in a chess club. The club holds a round-robin tournament in which every player plays against every other player exactly once. In how many games does a girl play against a different girl?
+36916 5 girls must play against 4 other girls = 20 games BUT 2 girls play in each game so divide by 2 = 10 games
or another way:
5 c 2 = 10 games
