I'm not too familiar with Zen, but questions like these are often meant to be nonsense questions with no answer. They push you to think harder and harder until you realize the futility of doing so, at which point you've found the "real" answer.

Previous poster either got this subtly wrong, or phrased it badly, or belongs to a tradition that I'm not familiar with, but a good story on this is the parable of the poisoned arrow: Someone gets shot by an arrow and his friend tells him they have to get to a hospital - the person shot starts worrying about what kind of poison it is, who shot him and why, if the hospital they are going to is any good, etc, etc - really he needs to go and get it treated RIGHT NOW and nothing else matters - he can answer all those questions after he's treated.

And I wouldn't say the zen koans are unanswerable, you can think of them like riddles that force you to think a different way than you normally do.