Math & Logic · Ages 18+
Riddle #201
Three switches outside a windowless room each control one of three light bulbs inside. You can flip the switches as many times as you like, but you may only enter the room once. How do you determine, with total certainty, which switch controls which bulb?
You solved this one before
Open-ended riddle: think it through, then reveal the answer.
Answer: Turn switch 1 on for several minutes, then turn it off. Turn switch 2 on and immediately enter the room. The lit bulb is switch 2's. The off-but-warm bulb is switch 1's. The off-and-cool bulb is switch 3's.