How do you answer this?

Answer:
Four
Step-by-step explanation:
If 2/5 of the marbles are red that’s equivalent to 4/10, if 1/10 is blue that means 5/10 are left over that are green. That means half the marbles are green, so 20 x 2 is 40. One tenth of forty is 4. Therefore, four marbles are blue.