This was a very simple puzzle, and therefore I guess I did not challenge enough minds. I got a correct answer from Mahi Saraf – well done Mahi! I would still encourage parents to show this puzzle to their children, it will be an interesting one for children.

I am taking the liberty of reproducing the answer from Mahi.

A=90kg, B=80kg, C=60kg, D=40kg, Supplies=20kg

1. D and C go
2. C comes back
3. A goes
4. D comes back
5. C and D go
6. C comes back
7. B and supplies go
8. D comes back
9. C and D go