Primary 5 – Maths Problem 1

Sandy has some dark and chocolates. If she eats 3 dark chocs, the ratio of the number of dark to white chocs is 5:4. If she eats 3 white chocs, the ratio of the number of dark to white is 7:5. What is the original number of dark chocs?

Yes, this is primary 5 maths problem. I would greatly appreciate it if someone can do this. It has to be done using Pri 5 methods – model or guess and check. Not simultaneous equation way!