A bag contains 8 white marbles, 4 black marbles, and 3 green marbles. You randomly pick one marble, then put it back and pick another marble. What is the probability that you picked a white marble followed by a black marble?
The probability of picking a white marble followed by a black marble is 8/15 * 4/15 = 32/225.

Here's the reasoning:

1. Since you're putting the marble back after each pick, this problem involves independent events.
2. First, let's find the probability of picking a white marble on the first try. There are 8 white marbles out of a total of 15 marbles (8 white + 4 black + 3 green), so the probability is 8/15.
3. Next, let's find the probability of picking a black marble on the second try. There are 4 black marbles out of a total of 15 marbles, so the probability is 4/15.
4. Since these events are independent, we can multiply their probabilities to find the overall probability: Probability = (8/15) * (4/15) = 32/225.