A round-robin tennis tournament consists of each player playing every other player exactly once.  How many matches will be held during an 8-person round-robin tennis tournament?
I need to find the number of ways to choose two players out of eight to play a match. This is a combination problem, since the order of the players does not matter. The formula for the number of combinations of n objects taken r at a time is nCr = n! / (r! (n - r)!). In this case, n = 8 and r = 2, so the number of matches is 8C2 = 8! / (2! 6!) = (8 * 7) / (2 * 1) = 28. 