Find the no. of ways you can fill a 3X3 grid(with four corner defined as a,b,c,d). if you have 3white balls and 6 black bolls.

• 3 white marbles can be placed in (3*3=9) grids in 9C3 ways & rest 6 marbles will be automatically filled
  so, no. of ways = 9C3
  
  if we start with black marbles then 6 black marbles can be filled in 9C6 ways & rest 3 will be automatically filled
  
  so, no. of ways = 9C6
  
  ans: 9C3=9C6=84
  
• 10 years agoHelpfull: Yes(0) No(0)