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    Question :
    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?
    Category Logical & Aptitude Interview Questions
    Rating (0.3) By 1504 users
    Added on 7/7/2005
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    To find the correct switch (1, 2, or 3), turn switch 1 to 'on' and leave it like that for a few minutes. After that you turn switch 1 back to 'off', and turn switch 2 to 'on'. Now enter the room. If the light bulb is lit, then you know that switch 2 is connected to it. If the bulb is not lit, then it has to be switch 1 or 3. Now touching for short the light bulb, will give you the answer: if the bulb is still hot, then switch 1 was the correct one; if the bulb is cold, then it has to be switch 3.

    first i will switch on the first switch and i will wait for few minutes and then switch that off.then i will switch on the second switch and i will visit the room.if light glows then it is the second switch.if it doesnt glow i will touch the bulb if it is heat then the first switch is the answer.if it is not heat then third switch is the answer

    Posted by: selva ganesh    

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    The switch which is frequently used will be somewhat dull in color when compared to those which were not used. by this we may find the correct ones.

    But this applies only if the switches were fitted long before.

    Posted by: venkatraman    

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    First I will turn on switch 1, then I will wait for some time. After that I will turn on switch 2 and check into the room for first time either the bulb lits or not. If the bulb lits then the problem is solved and if the bulb does not lits then I will check the bulb by touching either it is hot or cold. If it is cold then the third switch is correct and if it is hot then the first switch is correct.

    Posted by: Vikas    

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    First turn ON the two switches; Let it be Switch 1 and Switch 2, Now get inside the Room and check if the bulb is lit, if it has not lit then it is the Switch 3. Else it may be one of the two switches Switch 1 or 2.

    Posted by: srikanth    

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    Switch on all the three switches and check which one gets hot. That will be the correct switch.

    Posted by: Rajen    

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    1 switch is connected to a lamp.
    2 switches are connected to the bulb.
    Put on any 1 of the 3 switches and enter the room and see if the lamp is on. If the lamp is on, that means the other 2 switches are the onces connected to the bulb.

    Posted by: Brian Aguiar    

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    switch on bulb 1 wait for 10 min switch on bulb 2 as soon as u on 2 u enter and see if it not on 3 is connected.if not touch it if it is too hot means that 1 is connected other wise 2 is is d answer?

    Posted by: sowmyareddy    

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    Question is confusing ..not clear
    are there three bulbs or two bulbs and one lamp?
    how many chance are there to try ( do we swich only one button to find the answer )?

    Posted by: nilesh    

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    first turn on the first switch and leave it for a few turn off this switchand turn on the second switch and enter the enter the room and if the bulb is lit,then second is rigt.if it is hot the correct one is first and if cold the third one is correct.

    Posted by: anurag    

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