How to find it?


#1


#2

I will show you through illustration :
1 2 3 4 5 6 7 … m balls are there
there are total m+1 spaces between these balls see this : 1 | 2 | 3| 4 … m | … pipe illustrate the space .
Now these m+ 1 spaces can be placed within n bags. Take K ==1 , so conditions are now m>= n and k =1 ,
Hence answer is ( m-kn+n-1 , n-k ) . Option B