You are in a room with 3 switches. One of the switches controls a lamp with an incandescent lightbulb in a nearby room. You may flip the switches as many times as you like. You may only enter the room with the lamp once. You cannot see if the lamp is on from the room with the switches.
How can you determine which switch controls the lamp?
Number the switches #1, #2 and #3. Use the following strategy:
- Turn on switch #1.
- Wait a suitably long time (we will arbitrarily choose one hour).
- Turn off switch #1.
- Turn on switch #2.
- Enter the room with the lamp.
-
Examine the lamp:
- If the lamp is on, switch #2 controls the lamp.
- If the lamp is off, but the lightbulb is warm to the touch, switch #1 controls the lamp.
- Otherwise switch #3 controls the lamp.