- You’re standing in a hallway with three light switches on the wall, each of which turns on a different lamp inside a closed room. You can’t see inside the room, and you can’t open the door except to enter the room. You can enter the room only once, and when you do, all the lamps must be turned off. How can you tell which switch turns on which lamp?
- The water level in a reservoir is low, but doubles every day. It takes 60 days to fill the reservoir. How long does it take for the reservoir to become half full?
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