Answer: 7 marbles are green.
Explanation:
Since we have 12 marbles in total, 12/12 = 1. Since the fractions have denominators of 12 as well, we can easily tell there are 3 yellow marbles (3/12) and there are 2 blue marbles (2/12).
Lastly, we need to find how many are green. We can subtract the yellow and blue marbles from the total of 12 marbles.
12 - (3 + 2)
12 - (5)
7 marbles are green.