4 Switch problem

Four switches can be turned on or off. One is the light switch for the incandescent overhead light in the next room, which is initially off, but you don't know which. The other three switches do nothing. From the room with the switches in it, you can't see whether the light in the next room is turned on or off. You may flip the switches as often and as many times as you like, but once you enter the next room to check on the light, you must be able to say which switch controls the light without flipping the switches any further. (And you can't open the door without entering, either!) How can you determine which switch controls the light?


  1. let switches be s1,s2,s3,s4
    1)turn on s1 and s2 for 10 min and then turn them off
    2)now turn on s2 and s3 and enter the room
    a)if light is not on and the light is heated s1 is the correct switch
    b)if light is not on and the light is not heated s4 is the correct switch
    c)if light is on and the light is heated s2 is the correct switch
    d)if light is on and the light is not heated s3 is the correct switch

  2. @bhatti yes your logic is correct..:)


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