Here's another:
You are in the attic of a building. On the wall are three numbered light switches.
Down in the basement are three numbered light bulbs, each is connected to one switch. You don't know which switch is connected to which light. You do know that they are all off to start with.
You can do what you like with the switches, but once you leave the attic, the attic door will lock and you can't get back in.
The only place you can go to is the basement (three floors down).
Which bulb is connected to which switch?
I'm assuming all the switches are in the same position (down) to start with (On or off doesn't matter)...
Switches 1, 2, 3...
Flip switches 1 & 2 ... Leave them that way for about an hour... Flip switch 2 back.
Go to the basement...
If the lights were OFF to begin with...
You'll have switch 1's light on,
Switch 2's 1 lightbulb will be warm, &
switch 3's off.
If the lights were ON to begin with...
Switch 1's will be off,
Switch 2 & 3 will be on, but switch 2's light won't be as hot.
Thank you, thank you... I'll be here all week.