A bag contains 12 red marbles and 6 blue marbles. Two marbles are selected at random and without replacement. What is the probability that one marble is red and one is blue? Express your answer as a common fraction.
There are 18 marbles in total. Say we get a red, then blue. The prob of red is 12/18, and then blue is 6/17, since the red marble takes away one from 18. So 12/18 * 6/17 = 4/17. Do the same for blue, then red. You should get 4/17. Adding the two gets the answer of 8/17.
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