There are two rooms side by side in a corridor. Room A and Room B.
You are in Room A. You cannot see Room B or what is in it.
Room A has three electric switches on a table - switch 1, switch 2 and 3.
Each switch connects to a light bulb in Room B. But you do not know which switch connects to which light bulb.
Your mission, should you choose to accept it, is to identify which switch connects to which light bulb.
You are only allowed to visit Room B ONCE only. That is the time when you identify which light bulb connects to which switch. I repeat: you go to Room B and say, "this lamp is switch 1, this 2 and this 3".
Once you leave Room A you cannot go back there - you have to go to Room B to identify each light bulb is connected to which switch.
How do you do it?
PLEASE DO NOT READ THE ANSWER BELOW ... NOT YET
HERE ARE SOME CARTOONS TO ENTERTAIN YOU TILL YOU FIND THE ANSWER
Y O U R S E L F
OK ... If you give up ... here is the answer:
First you switch ON switch No. 1 for about ten minutes or so.
Then you switch No 1 OFF - and switch No. 2 ON.
Go to Room B.
The lit lamp is connected to switch No 2.
The warm lamp is connected to switch No. 1.
The cold lamp is connected to switch No. 3.