Question

using a circle with dots pattern to find the answer to : you are arranging a tennis tournament with nine players how many singles matcheswill be played among the nine players if each player plays the other players only once

Answer 1

Each player shall play against the other 8 players once, the answer must be 8+7+6+5+4+3+2+1=36 as far as I see, because the first player must play against eight, the next has played against the first already, so he must only play against 7, and so on ... On the basis of this you maybe can draw the "circle with dots pattern" ?