4. A contractor bids for two building projects. He estimates that the probability of winning the first project is 0.5 , the probability of winning the second is 0.3 and the probability of winning both projects is 0.2 .

1. Find the probability that he does not win either project.
2. Find the probability that he wins exactly one project.
3. Given that he does not win the first project, find the probability that he wins the second.
4. By calculation, determine whether or not winning the first contract and winning the second contract are independent events.