A singles tournament had six players Each player played ever

A singles tournament had six players. Each player played every other player only once, with no ties. If Helen won 4 games, Ines won 3 games, Janet won 2 games, Kendra won 2 games and Lara won 2 games, how many games did Monica win?

Solution

Since there are 6 players, a total of 5+4+3+2+1=15 games are played. So far, 4+3+2+2+2=13 games finished (one person won from each game), so Monica needs to win 15-13 = 2