How many matches played in a 17-team league

…when each team plays the others just once?

Wouldn’t that be (17 *16)/2 = 136 matches?

I guess I could explain why I think that’s the answer.

17 teams are each playing 16 opponents. You divide by two because 17 * 16 counts team X playing team Y, and it also counts team Y playing team X as another game.

e3

My colleague got the same answer a different, more mechanical way by adding 16+15+14 etc to get the same answer. He gave me a fish.

Your answer provides the principle. You have given me a fishing rod.