OG: If each of the 12 teams participating in a certain tournament plays exactly one game

[AbeNeedsAnswers]

If each of the 12 teams participating in a certain tournament plays exactly one game with each of the other teams, how many games will be played?

A. 144
B. 132
C. 66
D. 33
E. 23

C

[Scott@TargetTestPrep]

If each of the 12 teams participating in a certain tournament plays exactly one game with each of the other teams, how many games will be played?

A. 144
B. 132
C. 66
D. 33
E. 23

C

Solution:

The number of games played is 12C2 = 12! / (2! x 10!) = (12 x 11) / 2 = 66.

Answer: C

[Brent@GMATPrepNow]

If each of the 12 teams participating in a certain tournament plays exactly one game with each of the other teams, how many games will be played?

A. 144
B. 132
C. 66
D. 33
E. 23

C

A different approach:

There are 12 teams.
If we ask each team, "How many teams did you play?" we'll find that each team played 11 teams, which gives us a total of 132games (since 12 x 11 = 132).

From here we must recognize that each game has been COUNTED TWICE.
For example, if Team A and Team B play a game, then Team A counts it as a game, AND Team B counts it as a game.

So, to account for the DUPLICATION, we'll divide 132 by 2 to get 66

Answer: C

Cheers,
Brent