A light bulb is hanging in a room. Outside of the room there are three switches, of which only one is connected to the lamp. In the starting situation, all switches are 'off' and the bulb is not lit. If it is allowed to check in the room only once.How would you know which is the switch?

2 Answers on this Question

1. First of all we have to switch on the first switch and have to leave it for 6 or more minutes. After that, we have switch off it and second switch have to be turn on. Now immediately go to the room and touch the bulb. If the bulb is hot, first switch is the answer. If the bulb is already glowing, second one is the answer. if bulb is neither glowing nor hot, third one is the answer.

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2. Put switch 1 on and leave it on for 2 minutes, then switch it off.
   Put switch 2 on and leave it on, then walk into the room.
   If the light is on, the answer is switch 2.
   If the light is off but the bulb is warm when you feel it, the answer is switch 1.
   If the light is off and the bulb is cold when you feel it, the answer is switch 3.

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