HOW many solutions are dere to the equation:
x1+x2+x3+x4+x5=21
where xi=1,2,3,4,5, is a non-negative integer such that
c)0<=x1<=10
d)0<=x1<=3,1<=x2<4,and x3>=15?
These are done with generating functions.
d) Expand
The coefficient of answers your question.