Outside a room there are three light switches.
One of the switches is connected to a light bulb inside the room.
The room’s door is closed and you cannot see any light until you open the door.
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.)
Find out which switch controls the bulb inside the room??
On the first switch for about 10mins,
and then switch off the first one and switch on the second switch;
and then enter the room.
Three cases are possible
1. Bulb is on => 2nd switch is the answer.
2. Bulb is off and on touching the bulb, you will find bulb to be warm => 1st switch is the answer.
3. Bulb is off and on touching the bulb, you will find bulb to be normal(not warm) => 3rd bulb is the answer.