Bag has five red marbles, six blue marbles, and four black marbles. what is the probability of picking a red marble, replacing it, and then picking another red marble?

Add all the marbles together
5 (red) + 6 (blue) + 4 (black) = 15 marbles total
5 / 15 = 1/3
33% chance of picking a red marble
If you replace the red marble with another red marble, it would still be 33% since you're basically just putting the red marble back to re pick it (consecutively).
If you replaced the red marble, it would be 4 /15 since 5 - 1 = 4
4 / 15 = .27
27% of picking a red marble after replacing with a different color