There are three marbles in a bag. One is red and two are black. What is the probability of picking a black marble first, putting it back in the bag and then picking a black marble? Use the following probability to find the answer. Three binary trees, each with three levels. The first tree has two red nodes at the root and one blue node. The second tree has one red node at the root and two blue nodes. The third tree has two blue nodes at the root and one red node. All nodes have two children, except for the leaf nodes. a. What can we learn from this answer? This is the probability of picking a red marble and then another red marble. We wanted the probability of picking a red marble and then a black marble. b. a fraction two over three c. a fraction two over nine d. a fraction four over nine