In how many ways can 10 kindergarten children eat 30 cookies, if each child must eat at least one?
Give each child one cookie.
Now 10 children, 20 cookies.
So a+b+c+d+e+f+g+h+i+j=20
Result is (20+10-1) choose (10-1) = 29 C 9
= 10015005
+119 
