Here's a puzzle that's been asked in job interviews at Google, Goldman Sachs, and countless tech companies. It sounds 7 seconds impossible at first, but once you see the answer, you'll wonder how you didn't get it immediately. Ready? Here's the 14 seconds setup.
You're standing outside a closed room. Inside the room, there's a single light bulb. You can't see whether it's 21 seconds on or off. The door is completely sealed.
Outside the room, there are three light switches. One of them 28 seconds controls the bulb inside. The other two do nothing. Here's the catch.
You can flip the switches however you want, as 35 seconds many times as you want. But once you open the door and enter the room, you can never touch the switches again. You 43 seconds get one entry, one chance. How do you figure out with absolute certainty which 50 seconds switch controls the light bulb?
Take a second, think about it. Most people get stuck immediately. You've got three 58 seconds switches and only two possible states for the bulb, on or off. So, even if you walk in and the light is on, you've only 1 minute, 6 seconds narrowed it down to whichever switch you left in the on position.
That doesn't help if you flipped two of them on. And if the light is off, you've learned 1 minute, 15 seconds almost nothing. The math doesn't seem to work. Three possibilities, two outcomes.
1 minute, 21 seconds How can you possibly solve it in one trip? Here's where most people stay stuck. They're thinking in binary, on or 1 minute, 29 seconds off, light or dark. But that's not the only information a light bulb gives you.
1 minute, 35 seconds Think about what else a light bulb does when it's on. It gets hot. And that heat doesn't disappear the instant you turn 1 minute, 43 seconds it off. It lingers.
Which means a light bulb doesn't just have two states. It 1 minute, 49 seconds has three. on, off and cold, or off and warm. Now the solution clicks into 1 minute, 56 seconds place.
Turn on switch number one. Wait 5 minutes. Let that bulb, if it's connected, heat up. Then turn switch one off and immediately turn on switch two.
2 minutes, 8 seconds Now open the door. If the bulb is on, it's switch two. That's the one you left on. If the bulb is off, touch it.
If 2 minutes, 17 seconds it's warm, it's switch one, the one you had on for 5 minutes before turning off. 2 minutes, 22 seconds If the bulb is off and cold, it's switch three, the one you never touched. Three switches, three distinct outcomes, one 2 minutes, 31 seconds trip. Problem solved.
This riddle isn't really about light bulbs. It's about assumptions. Most people hear light bulb 2 minutes, 39 seconds and think only about light. They forget about heat.
They limit themselves to the obvious information and ignore 2 minutes, 46 seconds everything else the situation is giving them. That's why interviewers love this puzzle. They're not testing whether you 2 minutes, 53 seconds know the answer. They're testing whether you can step back from an impossible seeming problem and ask, "What am I not 3 minutes seeing?
What information is available that I haven't considered?" The best solutions often come from realizing the 3 minutes, 8 seconds question has more dimensions than you first assumed. On and off aren't your only options. There's a third state 3 minutes, 15 seconds hiding in plain sight. You just have to think beyond the binary.
Next time you're stuck on a problem, ask yourself, 3 minutes, 23 seconds "What else is this situation telling me that I'm not paying attention to? The answer might already be there. You just 3 minutes, 30 seconds have to feel for it. Think you would have solved it?" Let me know in the comments.
And if you want more puzzles like this, subscribe and hit the bell. 3 minutes, 39 seconds See you next time