MathNet 2015-part-05 — 191 problems (EN–VI) Question 142

In a football tournament participated $n$ teams. Each team played exactly one match with each other team. There was a total of $2015n$ matches played in the tournament. How many teams participated in the tournament?

(A) 2015 (B) 4029 (C) 4030 (D) 4031

(E) It is impossible to determine.