well that one provoked quite a bit of thought.
i've often though of the chicken/egg dilemma, but then i realised that dinosaurs laid eggs, so that sorted that out.
one question i asked as a kid was "what was there before the big bang?" and i reckon that one has caused a lot of thought in it's time... although because there's no way to prove anything about it, it's one that you eventually just have to give up on.
A friend of mine once asked me "how many molecules are there in that?" referring to a sample i had made in the [chemistry] lab. I spent some time working it out and it turned out to be about 9,000,000,000,000,000,000,000,000,000 (nine nonillian).
I asked my teacher what zero divided by zero was, and he didnt know. we agreed it was either zero (as zero divided by anything ought to be zero), one (as anything divided by itself is 1) or infinity (as anything dived by zero is infinite). I think generally people consider it to be zero but i still think about it
too many questions to ask and nowhere enough answers.
maybe the most thought provoking question is "how many questions are there?" or "how do i get the answers?"