Question
Question: Number of positive integral solution of x + y + z = 6 is...
Number of positive integral solution of x + y + z = 6 is
A
4 !
B
3 !
C
6!
D
10
Answer
10
Explanation
Solution
Number of positive integral solution of x+y+z = n is
Coefficient of xn in (x+x2 + x3 + ...)3 = Coefficient of xn (1+x+x2 + ...)3
= Coefficient of xn-3 in (1−x1)3
= Coefficient of xn-3 in (1-x)-3 = n−1Cn−3=n−1C2
Here n = 6
∴ Required solution = 5C2=10