A bag contains 9 marbles: 2 are green, 3 are red, and are blue. Shen chooses a marble at random, and without putting it back, chooses another one at random. What is the probability that both marbles he chooses are red? Write your answer as a fraction in simplest form.
There are a total of 9 marbles, so there are 9 choices for the first marble. If Shen chooses a red marble, there will be 2 red marbles left out of 8 total marbles for the second draw. Therefore, the probability of choosing 2 red marbles in a row is:
(3/9) * (2/8) = 1/12
So the probability is 1/12 written in simplest form.