A jar contains 5 blue marbles, 6 yellow marbles, and 4 green marbles. What is the probablity of randomly choosing a yellow marble, not replacing it, and then choosing a blue marble.

First, you need to choose a yellow marble. That is 6/15.

Next, you need to choose a blue marble. That is 5/14, because 1 yellow marble would have been "chosen" already.

So the probability altogether is 6/15 * 5/14 = 1/7, or about 14%.