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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?

Answer: 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.



Category Logical & Aptitude Interview Questions & Answers - Exam Mode / Learning Mode
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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?
Answer:

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. Source: CoolInterview.com


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 Source: CoolInterview.com

Answered by: selva ganesh | Date: | Contact selva ganesh Contact selva ganesh

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. Source: CoolInterview.com

Answered by: venkatraman | Date: 1/9/2010 | Contact venkatraman Contact venkatraman

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. Source: CoolInterview.com

Answered by: Vikas | Date: 2/6/2010 | Contact Vikas Contact Vikas

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. Source: CoolInterview.com

Answered by: srikanth | Date: 3/18/2010 | Contact srikanth Contact srikanth

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

Answered by: Rajen | Date: 4/19/2010 | Contact Rajen Contact Rajen

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. Source: CoolInterview.com

Answered by: Brian Aguiar | Date: 7/9/2010 | Contact Brian Aguiar Contact Brian Aguiar

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 connected.how is d answer? Source: CoolInterview.com

Answered by: sowmyareddy | Date: 7/20/2010 | Contact sowmyareddy Contact sowmyareddy


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