I that once in a technical interview and got the job (just paused for 30 seconds until the answer came to me). I think they expected a 15 minute process of problem solving.

If I recall correctly the question was something like:

You are sitting recording cars by their license plate as they drive down a road. You only have N spots on your worksheet. You can overwrite spots as many times as you need to. By the end of the day you must have an unbiased sampling of cars that have driven by you. How do you record the cars?