Question

five friends are having a tennis tournament .each friend will play the other four friends once.how many matches will be played

Answer 1

So there are 5 friends: a, b, c, d, and e.
Matches:
ab ac ad ae
bc bd be
cd ce
de

That answer would be, if I am not mistaken, 10.

Answer 2

To work it out...
Player 1 will play players: 2, 3, 4, 5
Player 2 will play players: 3, 4, 5
Player 3 will play players: 4, 5
Player 4 will play players: 5
All of player 5's matches have already been mentioned

Therefore, in answer to your question, I think 10 matches will be played.
Hope this helps.