Question : 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).
Your mission Jim, should you decide to accept it, is to go down to the basement and determine which bulb is connected to which switch.
Answer :
Turn two switches on, wait for a while, turn one of them off.
Walk down to the basement and feel both of the off lights bulbs.
The one which is warm is the one you have just switched off 🙂
The others are obvious.