Need help with a (simple) calculation

Hi
It would be great if someone could read through my calculation to see if I did it right.I made up the question to solve a real-world problem so have no answer to compare it to...
Question-> 100ml of dry quinoa(from the packet) swells to become 300ml cooked quinoa.I want to calculate how much quinoa I need to cook to make 1,200ml of quinoa milk with 20% quinoa,80% water.
I wrote the "equation"
20% of 1,200ml = (0.2)x(1,200ml) =240ml
(dry quinoa)x(3) = 240ml
dry quinoa=240ml/3
My answer : 80ml of dry quinoa is needed
Is this correct?
This is the only way I could think of figuring this out because I don't know how to calculate it using their weights,I don't know how much cooked quinoa weighs...
Thanks in advance!