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Thread: Puzzle

  1. #1
    Super Moderator PolicyWala's Avatar
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    Lightbulb Puzzle

    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.

    Question: 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?



  2. #2
    PolicyWala Fan rohit's Avatar
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    Switch on the first switch for a minute and then switch it off, then switch on the 2nd one and go inside the room, IF the bulb is still on, then 2nd one is the switch, if bulb is off and hot then 1st one is the switch and if bulb is off and not hot then 3rd one is the switch.

  3. #3
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    Turn on first switch for 15 minutes and now turn it off and turn on switch number 2 and move inside the room. If the bulb is on then it is connected to second switch and if it is off then go and touch it. If it is hot then it is connected to first switch else the bulb is connected to third switch.

  4. #4
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    switch 1 : place it ON for 1 hour. then switch it OFF.
    switch 2: Put it ON now.

    Go inside:
    if bulb is already lit: switch 2 is connected

    If its dark: touch and check the bulb:
    If it is hot: switch 1 is connected
    if it is not hot : Switch 3 is connected

  5. #5
    Super Moderator PolicyWala's Avatar
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    Thanks for your replies... Now Answer Time

    Switch on the first button and leave it on for 10 minutes, then switch it off and switch on the second button.Now enter the room, if bulb is on then second switch is the right one. If it is off then touch the bulb, if the bulb is hot then the first switch is the right one otherwise third switch is the right button


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