Explanation:
First, you want to find out how many total marbles there are. We know there are 6 red, 3 blue, and 5 green. So, 6+3+5=14 total marbles. Since there are 3 blue marbles, the probability of selecting a blue marble is 3/14. This is because you are selecting from a bag of 14 total marbles, 3 of which are the color you want.