Post:
You have three switches in one room and a single light bulb in another room. You are allowed to visit the room with the light bulb only once. How do you figure out which switch controls the bulb? Write your answer in the comments before looking at other answers.
Comment:
If this were an interview question, the correct response would be "Do you have any relevant questions for me? Because have a long list of things that more deserving of my precious time than to think about this!
You know, we're talking about how pointless a riddle it is. "Why can't I walk into the room more than once?" I've heard similar hiring riddles about things like "You've got ten ethernet cables that run the length of a long hallway. They're not marked at either end, what's the most efficient way of finding out which is which?"
And you know what? If I'm hiring a networking guy, I don't want him to deliver me an "ooh I know this one" answer to that, I want him to tell me he's got a cable tester with several remote probes so he can figure that out in a small number of trips. Maybe show me how he can hook a couple together with a coupler and use the cable length function to shave a couple of trips off. Not recite a memorized brain teaser answer.
Thr difference in phrasing is that your question presents a reasonable objective rather than an unreasonable constraint. You're also asking something subject-specific from someone who ought to be versed in that subject. That's not a riddle, it's a task you're expecting your hire to be capable of.