# How can you determine with which of the three switches the light bulb can be switched on?

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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 to see if the bulb is lit or not (this is not visible from the outside), how can you determine with which of the three switches the light bulb can be switched on?

posted Apr 27, 2014

+1 vote

Step 1. Switch on any bulb for 1 min lets say first one.
Step 2. Switch on the second bulb and go inside. there will be three cases :

case 1. If bulb is on then second switch is correct one.
case 2. If bulb is off then touch bulb it if it is hot then first one was the correct switch.
case 3. if both above cases are not true then third one the right switch.

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