Mark the correct alternative in the following :
The coefficient of 
in the expansion of 
is.
Given:
(1+x)21+(1+x)22+...+(1+x)30
Coefficient of x5in any expansion = 
; i.e. nC5
So, coefficient of x5 in above expansion = 21C5 + 22C5 + 23C5 +…+ 30C5
1