back office interview questions shared by candidates
You are in a room with 3 switches which correspond to 3 bulbs in another room and you don't know which switch corresponds to which bulb. You can only enter the room with the bulbs once. You can NOT use any external equipment (power supplies, resistors, etc.). How do you find out which bulb corresponds to which switch?
Turn on 2 switches. Turn one switch off after a few minutes. Enter room with bulbs. The bulb that is on is the only switch that is on. The bulb that is off but hot, is the switch that has been turned off. The bulb that is off and cold is the third switch.
Turn on switch A for 1 minute. Turn it off. Turn on switch B. Enter the room with the bulbs. The hot bulb is A The lit bulb is B The dark bulb is C
Turn switch A leave it on for 1/2 minutes and turn it off then turn on switch B. Now goto the room, the one Hot is A, Cold(or not Hot) is C, the bulb thats on is B.
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