Distribute $1000 to 4 persons (in unit of $100) (a) no restriction (b) at least $100 for anyone (c) at least $100 for anyone, Sam has at least $500.
There can be several solutions for this question,here is my take:
Consider A,B,C and Sam as the 4 people. Sam compulsorily gets 500$,then let A get 300$,B gets 100$ and C gets 100$. In this way all the necessary conditions are fulfilled. You can also have some other solution for this problem.