Which switch controls the bulb??


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 ??

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  • 2 Answer(s)

    Set the first switches on for abt 10min, and then switch on the second switch and then enter the room.
    Three cases are possible
    1.Bulb is on => second switch is the ans
    2.Bulb is off and on touching bulb , you will find bulb to be warm
    =>1st switch is the ans.
    3.Bulb is off and on touching second bulb , you will find bulb to be normal(not warm)
    =>3rd bulb is the ans.

    John123 Expert Answered on 26th July 2015.
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    This question was asked to me in my Deloitte Interview.It follows as:

    1)First ON the first switch. Wait for some time .
    2)Now Switch OFF the first switch and ON the second switch.
    3)Now go to the room and check if the bulb is glowing (Which means that Second Switch is answer)  , or it is warm (which means First Switch is answer) or Neither(Which means third is the answer).

    Tip::Never tell the answer directly .Try to tell many approaches and at the end or in middle tell the answer you can try this approach too.

    Ganesh Patel Scholar Answered on 26th November 2015.
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