Answer:
If 3/5 of your marbles are green and the rest are yellow then you would want to subtract your total which is 5/5 by 3/5, to find the total number of yellow marbles.
5/5-3/5=2/5
That means that 2/5 of your marbles are yellow.
You now want to double that number so 2/5+2/5=4/5.
The fraction of marbles that are yellow would be 4/5.
Hope this helps ;)