There are, in a certain league, 20 teams, and each team face another team for a total of 10 times. How many games are played in the season?  Answers
A) 1900  B) 3600  C) 2400  D) 180  E) 5400

Rationale: "1 st team : 190 2 nd team : 180 3 rd team : 170 similarly the last team will play 0 therefore ( 190 + 180 + 170 . . . . 10 ) 10 ( 19 + 18 + 17 + 16 . . . . 1 ) 10 ( n ( n + 1 ) / 2 ) = 10 ( 19 * 20 / 2 ) = 1900 answer : a"
Answer: A