probability of marbles

Question

Two marbles are drawn without replacement from a box with 3 white, 2 green, 2 red and 1 blue. Find the probability that the second marble is blue when given that the first marble is red.

Answer 1

Now that there is "WITHOUT REPLACEMENT," after the red marble is drawn--and not replaced--there are only 7 marbles now. Out of those 7, only one is blue, so the probability is 1/7