Outside a room there are three light switches. One of switch is connected to a light bulb inside the room.
Each of the three switches can be either 'ON' or 'OFF'.

You are allowed to set each switch the way you want it and then enter the room(note: you can enter the room only once)

Your task is to then determine which switch controls the bulb ??

• Let the three switches be A,B and C. I will switch on 'A'. Then I will switch on 'B' and will wait for a few minutes. Then switch 'B' will be switched off. Then I will enter the room. Please note that switch 'C' will always be turned off. There can be three occurances:
  
  1) The bulb is lit: In this case, I am sure that switch 'A' is connected to the bulb.
  2) The bulb is not lit and it is hot (after touching it): In this case, I am sure that switch 'B' is connected to the bulb as I have switched off 'B' couple of seconds ago.
  3) The bulb is not lit and cold: In this case, I can get sure that switch 'C' is connected to the bulb.
• 11 years agoHelpfull: Yes(5) No(1)