Bored

[threaded]

In your cellar there are three light switches in the OFF position. Each switch controls 1 of 3 light bulbs on floor above.

You may move any of the switches but you may only go upstairs to inspect the bulbs one time. How can you determine the switch for each bulb with one inspection??

Switch one on, wait five minutes. Switch it off, and switch another one on. And up the stairs to see which light it was.

If there is a light on, then you've found it.
If there isn't one on, check which light bulb is warm, then you've found it.