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?

• 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 ..
• 9 years agoHelpfull: Yes(16) No(2)
• since every team playing against other team,so
  according to question nC2=21
  
  now solving it
  n^2-n-42=0
  n=-6,7.
  since n nvr be -ve .
  so the correct answer is 7.
• 9 years agoHelpfull: Yes(11) No(0)
• ans is 7
  i.e 6+5+4+3+2+1=21
• 9 years agoHelpfull: Yes(3) No(2)
• n(n+1)/2=210
• 9 years agoHelpfull: Yes(1) No(5)
• there are 7 teams
  1 2 3 4 5 6 7
  
  1 can play 6 matches
  2 can play 5 matches
  and so on 6 can play 1 match with 7
  then finally we get
  6+5+4+3+2+1=21
• 9 years agoHelpfull: Yes(1) No(0)
• The actual formula is:n(n-1)/2
  Here,n(n-1)=42
  So,n=7;(neglecting -ve value of n)
• 9 years agoHelpfull: Yes(0) No(0)