Fifteen years was a long time to be stranded anywhere, particularly somewhere as mind-boggingly dull as Earth. - Douglas Adams

I think the problem, to be quite honest with you, is that you've never actually known what the question is.

POPULATION: None. It is known that there are an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not every one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so the average population of all the planets in the Universe can be said to be zero. From this it follows that the population of the whole Universe is also zero, and that any people you may meet from time to time are merely the products of a deranged imagination.

After a while he played with the pencil and the paper again and was delighted when he discovered how to make a mark with the one on the other. Various noises continued outside, but he didn't know whether they were real or not. He then talked to his table for a week to see how it would react.