No of ways you can fill a 3*3 grid (with 4 corners marked as a,b,c,d) if you have 3 white and 6 black marbles.
Option
a) 9C3
b) 6C3
c) 9C3+6C3
d) (9C3+6C3)/3!

• 3 white marbles can be filled in (3*3=9) grids in 9C3 ways & rest 6 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
  
  2nd mtd,
  we have to filled 3*3=9 grid with 3 of white & 6 of black marbles
  so, no. of ways = 9!/(3!*6!) = 9C3 = 9C6 = 84
• 10 years agoHelpfull: Yes(42) No(3)
• first fill 3 grids using white marbles by 9C3.Then,the remaining grids will be filled by black marbles i.e. 6 grids to be filled by 6 marbles,places here are 6,therefore,combinations will be 6C6.so the final answer is 9C3*6C6=9C3.
• 10 years agoHelpfull: Yes(5) No(0)
• .First let us take 3 white = 9!/(9-3)! 2. Let us take remaining 6 black - 6! ways we can place them 3. when we add both = 9!/(9-3)! * 6 ! = 9!
• 10 years agoHelpfull: Yes(1) No(1)
• 9C3 i guess...as u only have to select spots for 3 white marbles and black will be automatically be at other 6 spots.
• 10 years agoHelpfull: Yes(0) No(1)
• 9C3
  as we all know the Marbles are same color
• 10 years agoHelpfull: Yes(0) No(0)
• 9c3
  is the best way for marbles
• 10 years agoHelpfull: Yes(0) No(2)
• No. of ways to arrange 9 marbles in 3*3 grid = 9!
  here 3 marbles are white and 6 are black
  so
  required arrangement = 9!/(3!*6!) = 9C3 = 84
• 10 years agoHelpfull: Yes(0) No(0)