What is the total number of marbles in the box?

Probability of drawing a green marble from the box is $$\frac{1}{5}$$
We know that the number of yellow marbles are twice as many as green marbles. Hence the probability of yellow marbles would be $$\frac{2}{5}$$
Since there are only 3 types of marbles in the box, so the probability of red marbles would be $$ 1 - \frac{1}{5} - \frac{2}{5} = \frac{2}{5}$$
Let the total number of marbles be k, then we have
$$\frac{10}{k} = \frac{2}{5}$$
=> k = 25