> I have two children. Child A is a boy, born on a Tuesday, what is the probability that child B is a boy? We have no knowledge of child B so the probability i

> I have two children. Child A is a boy, born on a Tuesday, what is the probability that child B is a boy? We have no knowledge of child B so the probability is even for it being a boy or a girl. > I have two children, at least one of them is a boy who is born on a Tuesday. What is the probability that I have two boys? We have incomplete knowledge of both children, we are constraining a probability space in 2 dimensions (i.e. the 2 children) rather than refining it down to 1 dimension as before. In this case the probability is 13/27 as these tables (http://news.ycombinator.com/item?id=3290349 http://news.ycombinator.com/item?id=3290349) nicely show. When the father says "one is a son born on a tuesday" this can be read as him selecting a child and then asking you about the second or as giving you some information that can apply to either child and then asking you about both. In my opinion the language used leads much more easily to the first interpretation, this is the reason surely for the confusion.