There are N players in a tennis tournament. Assuming the initial pairings are done randomly, what are the odds that a certain pair will play each other?

(In reply to

re(2): I undestood right? - no, WRONG. by pcbouhid)

If the odds of A and B playing in the first round were 1/C(N,2) as you
say, then the odds of A and C would be the same, and so A and D, A and
E, etc.

However, then the odds of A playing ANYBODY would be (N-1) times 1/C(N,2), and that doesn't equal 1!

A can play any of the other N-1 players in the first round, so the odds of him playing anybody in particular are 1/(N-1)