Alright, we've all seen the first couple of these, but the third one is kind of interesting. 1. A man has two children, the older of which is a son. What is the probability that he has two sons? 2. A man has two children, at least one of which is a son. What is the probability that he has two sons? 3. A man has two children, one of which is a son who was born on a Sunday. What is the probability that he has two sons?