Honestly, the first time someone asked me why manhole covers are round, I almost walked out. It felt like a prank. But here's the thing: brain teasers for interviews aren't actually about the answer. Most people think they need to be a math genius or a logic wizard to survive these sessions at companies like Google or Goldman Sachs. They don't. They just need to show how they think.
Laszlo Bock, the former Senior VP of People Operations at Google, famously admitted to the New York Times that brain teasers are mostly a waste of time for predicting how well someone will actually do the job. Despite that, they still haunt the halls of finance, engineering, and consulting. Why? Because recruiters are human. They want to see you sweat, sure, but they mostly want to see if you crumble when a problem doesn't have a clear manual.
It’s about the "grit" of your logic.
The Myth of the Right Answer
If you spend your night memorizing the "correct" response to the 25 horses puzzle, you're doing it wrong. Interviewers have heard the rehearsed answers a thousand times. They're bored. What actually gets a hiring manager’s attention is the messy, loud, verbalized process of you navigating a dark room.
Think about the classic: "How many piano tuners are there in Chicago?"
This is a Fermi problem. Enrico Fermi, the physicist, was obsessed with these back-of-the-envelope calculations. You aren't supposed to know the census data for piano tuners. You're supposed to estimate the population of Chicago (maybe 2.7 million), guess how many households own a piano (1 in 20?), and figure out how often a piano needs tuning. If you just blurt out "200," you’ve failed, even if the answer is actually 200. You have to show the scaffolding.
The math doesn't have to be perfect. The logic does.
Why Companies Still Use Brain Teasers for Interviews
Tech giants have shifted away from the "riddle" style, but "estimation" and "case-based" teasers are thriving. In 2026, the focus has moved toward algorithmic thinking. They want to see if you can break a massive, terrifying problem into bite-sized, executable pieces.
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Imagine you're at a hedge fund. They ask: "If I flip a coin until I get two heads in a row, what's the expected number of flips?" This isn't just a trick; it's a test of your comfort with probability under pressure. It's about whether you panic when the numbers get fuzzy.
Jane Street and Susquehanna are notorious for this. They aren't looking for a "culture fit" in the traditional sense; they are looking for "probability fit." They want people who see the world in expected values. If you can't handle a brain teaser about marbles in a jar, how will you handle a ten-million-dollar trade moving against you in milliseconds?
The Anatomy of a Logic Trap
Most brain teasers for interviews fall into three buckets.
First, you've got the Lateral Thinking puzzles. These are the ones that sound like a riddle. "A man is found dead in the middle of a desert with an unopened package next to him. What happened?" (The package was a parachute). These are actually the least helpful for jobs, and most modern firms have ditched them because they rely on a single "aha!" moment rather than sustained reasoning.
Second, there are Estimation/Fermi Problems. These are the gold standard.
- "How many tennis balls fit in a Boeing 747?"
- "What is the annual revenue of a specific Starbucks in Manhattan?"
- "How many gallons of white paint are sold in the US every year?"
Third, you have Probability and Market Sizing. These are common in consulting (McKinsey, BCG) and finance. They want to see if you understand how markets scale. If you're interviewing for a product role at a tech firm, they might ask how you'd estimate the cost of storing every photo on Instagram. It sounds like a brain teaser, but it’s actually a capacity planning exercise.
Breaking Down the "Clock Hands" Problem
Let's look at a common one: "How many times a day do the hands of a clock overlap?"
Most people say 24. It’s a logical guess. 12 hours in a cycle, two cycles a day, right? Wrong.
If you actually visualize the clock, the hands overlap roughly once an hour, but because the hour hand is also moving, the "catch-up" takes longer than 60 minutes. They overlap at 12:00, then not again until about 1:05, then 2:11, and so on. By the time you get around the circle, you've lost one overlap per 12-hour cycle.
The answer is 22.
But again—and I cannot stress this enough—the person across the table doesn't care if you say 22 or 21 or 23. They care if you realize that the hour hand isn't stationary. They want to see you use your fingers to mimic the clock hands. They want to hear you say, "Wait, if the hour hand moves, the minute hand has to travel further to catch it."
That realization is the "hireable" moment.
The "I Don't Know" Strategy
What happens when your brain just... stops? It happens to everyone. The silence in the room gets heavy. You start sweating.
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The worst thing you can do is sit there in silence for three minutes.
Talk. Even if what you’re saying feels stupid. "Okay, I'm thinking about the surface area of the plane versus the volume of a tennis ball. I know a tennis ball is roughly 2.7 inches in diameter, but there's going to be air gaps between them because they're spheres."
By doing this, you're giving the interviewer a "hook" to help you. Often, if they see you're on a productive path, they'll give you a nudge. "Don't worry about the seats inside the plane, just assume it's an empty shell." Now you're collaborating. You’ve turned an interrogation into a meeting. That is exactly what they want to see.
How to Practice Without Losing Your Mind
Don't just read lists of riddles. That's a waste of time. Instead, start looking at the world through a "size" lens.
When you're standing in line at a grocery store, try to estimate the daily turnover of that store. How many registers are there? What's the average basket size? How many people per hour?
If you can do that comfortably, no brain teaser for interviews will scare you. You’re building a mental muscle for approximation.
Real-World Examples to Chew On
- The Lightbulb Puzzle: You have three switches outside a closed door. One controls a bulb inside. You can only enter the room once. How do you know which switch is which? (Turn one on for ten minutes, turn it off, turn the second one on, and go in. If the bulb is off but hot, it's the first switch).
- The Bridge and Torch: Four people need to cross a bridge at night. They only have one torch, and the bridge can only hold two people. Each person walks at a different speed (1, 2, 5, and 10 minutes). How do they all get across in 17 minutes? (The trick is sending the two slowest people together so their times overlap).
These aren't just for fun. They test your ability to optimize resources. In the bridge puzzle, the "torch" is the bottleneck. In business, identifying the bottleneck is often the difference between a profitable quarter and a disaster.
The Shift Toward "Work Sample" Teasers
By 2026, the most sophisticated companies have swapped the "manhole cover" questions for "mini-architecture" questions.
Instead of asking why tennis balls are fuzzy, they’ll ask: "How would you design a system to detect fraudulent credit card transactions in real-time?"
This is still a brain teaser. It’s open-ended, high-pressure, and requires logical leaps. But it’s grounded in the reality of the job. You still need to use the same framework:
- Clarify the constraints.
- Make reasonable assumptions.
- Break it into stages (Input -> Processing -> Output).
- Identify the risks.
Actionable Steps for Your Next Interview
Stop viewing the interview as a test you pass or fail. View it as a whiteboard session with a future colleague.
First, always bring a pen and paper. Drawing a diagram or jotting down your assumptions makes you look organized and gives your brain a visual anchor. It prevents you from looping on the same thought.
Second, ask clarifying questions. If they ask how many cars are in Seattle, ask if they mean registered vehicles or cars physically on the road at a given time. This shows you understand that data is nuanced.
Third, check your work out loud. If your final estimate for a market size comes out to $50 trillion, and the US GDP is only $27 trillion, stop. Say, "That number feels way too high. Let me go back and see where my assumption tripped up." Admitting a mistake in real-time is a massive green flag for employers. It shows you have a "sanity check" mechanism.
Finally, don't forget to smile. It sounds cheesy, but these puzzles are designed to be stressful. If you can tackle a difficult logic problem with a bit of humor and a calm demeanor, you're proving you won't be a nightmare to work with when a real project goes sideways.
The goal isn't to be a calculator. The goal is to be a thinker who is easy to think with.
Refine your estimation skills by practicing with everyday objects—the number of bricks in a wall, the volume of water in a pool, or the number of people wearing blue shirts in a stadium. Once the "how to think" becomes second nature, the "what to say" follows effortlessly.