I interpreted it the "wrong" way too. I thought about it like this: Instead of telling me that there is a girl or a boy tell me only that "1 + 1 = 2" and then ask me what the odds of the mothers child are for being a boy. I'll say 50%. I don't care what the state of some other child, I just care what the state of the unknown is. Now, if he had said, "you ask a woman that has a random assortment of children if she has at least 1 girl and she answers 'yes', what are the odds that the other is a boy" THEN I would be fine with the problem.