There is an unlimited stock of blue, red, white, and grey coloured balls. What is the number of ways of selecting 12 balls from the stocks? Choose the correct choice from the following answers.
A) 735
B) 445
C) 455
D) 475
E) 854
Let us say that we have selected 'x1' blue balls, 'x2' red balls, 'x3' white balls and 'x4' grey coloured balls.   This means, x1+x2+x3+x4 = 12   Now, for an intance, 1+2+3+6 can be an answer. 0+0+0+12 can also be another answer   Hence, we need to find the non-negative integral solution for the equation   x1+x2+x3+x4 = n is   (n+k-1)455(k-1)   Here, n=12 and k=4   (12+4-1)455(4-1) = 154553 = 455   ANSWER:455
<result>C</result>
There is an unlimited stock of blue, red, white, and grey coloured balls. What is the number of ways of selecting 12 balls from the stocks?