The problem:

There's a box with a hole at each end, and there's a rabbit in the box. The rabbit sticks his head out of the hole in one end, and a minute later he sticks it out the other end. Half a minute later, his head appears at the opposite end, a fourth of a minute later it appears at the end opposite to that one, an eighth of a minute later, etc., etc.

How long will it take before the rabbit sticks its head out of both ends of the box at the same time?

In theory, two minutes.

In practice, no answer is possible unless you split hares.