A set of football matches is to be organized in a "round-robin" fashion, i.e., every
participating team plays a match against every other team once and only once. If 21
matches are totally played, how many teams participated?
Choose one.
A) 4  B) 5  C) 6  D) 7  E) 8
2 ways to solve this problem..   summation(x)=n(n-1)/2   n(n-1)/2=21;   n^2-n-42=0   factors : 7,-6   Ans : 7   ANSWER:7
<result>D</result>
A set of football matches is to be organized in a "round-robin" fashion, i.e., every
participating team plays a match against every other team once and only once. If 21
matches are totally played, how many teams participated?