Exercise 2.5. We have two urns. The first urn contains three balls labeled 1, 2 and 3. The second urn contains four balls labeled 2, 3, 4 and 5. We choose one of the urns randomly, so that the probability of choosing the first one is 1/5 and the probability of choosing the second is 4/5. Then we sample one ball (uniformly at random) from the chosen urn. What is the probability that we picked a ball labeled 2?