[alesua93]

Fair enough. I understand where you're coming from, at the end of the day I guess it depends on the context and the way the question is presented (left-field questions such as this one can be somewhat fun to try to answer and hypothesize about, if the interviewer creates a friendly environment to do so)

[Unklejoe]

I hear ya. I would definitely not disqualify someone for not knowing the answer.

In fact, someone who is able to sort of work through the problem on the spot may even be preferable to someone who just knows the answer because they happened to read Wikipedia the week before.