Neurology Teacher Question:
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Suppose there are three light switches outside a room. Inside is a single light bulb, controlled by one of the three switches. You need to determine which switch operates the bulb. You can turn the switches on and off as many times as you wish (they are all off to begin with), but may only enter the room once. There is no one there to help you. The door to the room is closed, and there are no windows, so you cannot see inside. How can you discover which switch operates the bulb?


Answer #1
Do the following steps:
☛ 1. Turn ON two switches, and leave one OFF.
☛ 2. Wait a few minutes.
☛ 3. Turn one switch from ON to OFF. One is now ON and two are OFF
☛ 4. Enter the room. - If the light is ON, it is controlled by the switch you left ON. - If the light bulb is OFF, touch it. If it is warm it is controlled by the switch you turned ON and OFF. If it is cold, it is controlled by the switch you never turned on.

Answer #2
Open the door and hold it open, turn the switches on and off one at a time to determine which one turns the light on.

Answer #3
1. Keep the door closed and switch on switch A for a sufficiently long time.
2. Switch A off, then switch B on, and immediately open the door. If the bulb lights up, then the answer is B.
3. If not, go into the room and touch the bulb. If it's hot, then the answer is A. If not, the answer is C.

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