Mary has 12 marbles. 3/12 marbles. are yellow and 2/12 of the marbles are blue. the rest of the marbles are green. how many marbles are green? ? explain how you know.

This simply means that 3 out of the 12 are yellow and 2 out of 12 are blue. So add the blue and yellow together to get 5, then subtract 5 from 12 and get 7. There is 7 green marbles

The variables should add up to equal 1