++ [ originally posted by Erik
] ++
Oohh nostalgia then

I've got one for you:
There are two rooms. One of them has three lamps, the other one has three light switches connected to the lamps in the other room.
You are in the room with the light switches and it is impossible for you to look into the other room.
You can only leave ONE lightswitch switched on and go into the other room ONCE to check which lamp you switched on.
How do you find out which lightswitches are connected to each of the lamps?