A person goes in for an examination in which there are four papers with a maximum of m marks from each paper. The number of ways in which one can get 2m marks is
The required number
=Coeff
of x2m in (1−xm+1)4(1−x)−4=
Coeff of x2m in (x0+x1+…+xm)4
=(2m+1)(2m+2)(2m+3)6
−4m(m+1)(m+2)6
=(m+1)(2m2+4m+3)3