I posted this in the comments but then decided it should be up here. Sorry in advance for the inarticulate wording, but hopefully it will make sense. It’s a brainteaser, and it’s hard:
There are two rooms, one of them has three light switches, the other has three lightbulbs and you don’t know which bulb goes with which switch. you can do whatever you want to the switches but you must then go into the room with the bulbs and figure out which goes with which. (you can’t go back into the room with the switches). how can it be done?