Latest / Interview Prep with Fexingo: Behavioral Questions, Case Studies, and Hiring Manager Insights / How to Answer the Brainteaser Question in Interviews
Transcript
- Lucas: So you're in an interview, things are going fine, and then the hiring manager says — 'How many piano tuners are there in Chicago?' Luna: Oh, that classic. The brainteaser. I've had that one, and I remember just staring at the table for what felt like a full minute. Lucas: Right. And most people panic because they think the interviewer wants the exact number. But the real test is whether you can structure a logical thought process on the spot, out loud, without freezing. Luna: Exactly. It's not about the answer — it's about the reasoning. So let's talk about how to actually handle these without your brain short-circuiting. Lucas: Let's start with why companies still ask them. A 2025 Glassdoor survey found that about one in five interviewers at top consulting firms and tech companies still include a brainteaser or guesstimate question. But get this — only 18 percent of those interviewers said they actually care about the final number. Luna: Wow. So 82 percent are using it as a stress test or a thinking-style diagnostic. Lucas: Exactly. They want to see how you handle ambiguity, whether you can break a vague problem into manageable pieces, and whether you keep your composure when you don't have all the data. So the first rule is: don't try to be right. Try to be clear. Luna: That's a huge mindset shift. Most of us are trained to give the correct answer, not to narrate our confusion. Lucas: Right. So let's walk through a framework. I like to think of it in four steps. Step one: clarify the question. Step two: state your assumptions. Step three: build the math step by step. Step four: give a range, not a single number. Luna: And do all of that out loud, right? The interviewer can't read your mind. Lucas: Exactly. They need to hear your thought process. So let's use a concrete example that's common in interviews: 'How many golf balls fit in a Boeing 747?' Luna: Oh, that's a famous one. I've heard it from friends who interviewed at McKinsey and Google. Lucas: It's everywhere. So step one — clarify. You might say: 'I assume you mean standard golf balls, regulation size, and the interior volume of a 747, not including cargo holds or the cockpit? And are we talking packed efficiently or loosely?' Luna: That immediately shows you're not just guessing. You're defining the problem. Lucas: Exactly. And the interviewer will usually say 'packed as efficiently as possible, standard golf balls, and yes, the passenger cabin plus cargo hold.' So now you have a boundary. Step two — state your assumptions. I'd say something like: 'I'm going to assume a 747 has about 400 seats, and each seat takes up roughly the space of a typical airline seat — let's say 2 feet wide by 3 feet deep by 4 feet tall. That's 24 cubic feet per seat. So 400 seats times 24 cubic feet is 9,600 cubic feet.' Luna: Wait, you're also assuming the whole interior is just seats? What about aisles, galleys, lavatories? Luna: Right, you'd need to add some extra volume there. I might say: 'I'll add about 20 percent for aisles and other open space, so roughly 11,500 cubic feet.' Or if you want to be more precise, you could estimate the cylinder volume of the fuselage. But the interviewer doesn't care about perfection — they care that you're adjusting. Luna: So then step three — the math. A golf ball is about 1.68 inches in diameter. In feet, that's 0.14 feet. The volume of a sphere is four-thirds pi r cubed. But for packing, you can approximate a cube around each ball: 0.14 feet cubed is about 0.0027 cubic feet per ball. Lucas: But you can't pack spheres perfectly. The densest packing of spheres is about 74 percent efficiency. So you multiply 11,500 cubic feet by 0.74, which gives you about 8,500 cubic feet of actual golf ball volume. Then divide by 0.0027, and you get roughly 3.1 million golf balls. Luna: Three point one million. That's a number. But it's not the point. Lucas: Exactly. The point is you walked through it logically. And then step four — give a range. I'd say: 'So my estimate is between 2.5 and 3.5 million golf balls, depending on how much space I accounted for aisles and the exact packing efficiency.' That shows you understand your assumptions have uncertainty. Luna: I love that. It's not about being right — it's about being reasonable and transparent. And I think the biggest mistake people make is they try to pull a number out of thin air without showing their work. Lucas: That's the number one error. The second is getting defensive when the interviewer pushes back. If they say 'Why did you use 400 seats?', don't freeze. Just say: 'That's my initial assumption. If you have a better number, I can adjust.' It shows flexibility. Luna: So let's talk about a different type of brainteaser — not a guesstimate, but a logic puzzle. Like, 'You have a 3-gallon jug and a 5-gallon jug. How do you measure exactly 4 gallons?' Lucas: Oh, the water jug problem. That one's classic in tech interviews, especially at companies like Amazon and Microsoft. The key there is to think in terms of state transitions. You start with two empty jugs. You can fill, empty, or pour from one to the other. Write it out on a whiteboard or narrate each step. Luna: And again, the answer isn't the only thing. They want to see if you can systematically explore possibilities without getting frustrated. Lucas: Right. So for the 3 and 5 gallon jugs, one solution: fill the 5-gallon jug. Pour from the 5 into the 3 until the 3 is full — that leaves 2 gallons in the 5. Empty the 3. Pour the remaining 2 gallons from the 5 into the 3. Then fill the 5 again. Pour from the 5 into the 3 until the 3 is full — that takes 1 gallon, leaving 4 in the 5. Done. Luna: That's clear. And if you narrate that out loud, the interviewer can follow your logic even if you pause. Lucas: Exactly. And here's a tip: if you get stuck, say 'Let me think about this for a moment.' Silence is fine — as long as you don't stay silent for too long. Ten seconds of thinking is okay. Thirty seconds is a problem. Luna: So what about brainteasers that seem completely random? Like 'Why are manhole covers round?' Lucas: That one is actually a classic that Microsoft used to ask. And there's a famous answer: a round cover can't fall through its own hole because the diameter is constant. A square cover can be turned diagonally and dropped in. But again, the interviewer might be testing your ability to think about design trade-offs — not just geometry. Luna: So you could also talk about manufacturing or safety? Like round covers are easier to roll? Lucas: Exactly. There's no single right answer. The interviewer wants to see that you can generate multiple valid reasons and prioritize them. So you might say: 'The primary reason is structural — a circle can't fall in. But also, round covers are easier to manufacture and transport. And they don't need to be aligned when you put them back.' That shows breadth. Luna: That's a great strategy. And honestly, a lot of candidates don't realize that most brainteasers are just a test of how you handle the unexpected. It's not about the answer — it's about the conversation. Lucas: Right. And one more thing — preparation matters. You can't memorize answers, but you can practice the structure. There are books and online resources with lists of common guesstimates and logic puzzles. Practice three or four out loud with a friend. Get comfortable saying 'I'm going to assume...' and 'That leads me to...'. Luna: And if you've got an interview coming up, this kind of practice can seriously reduce the anxiety. Because you've already done it in a low-stakes setting. Lucas: Exactly. And look — if this episode helped you think through a career move or decision, that's the kind of thing that keeps us going. We keep the show ad-free and listener-supported. If today was worth a coffee to you, that's the link — buy me a coffee dot com slash fexingo. No pressure, just a way to say it mattered. Luna: Yeah, honestly it's a small thing that makes a big difference for us. We appreciate everyone who's ever chipped in. Lucas: Alright, back to brainteasers. One last tip: after you give your answer, ask the interviewer a question. Like, 'Does that align with how you approach these problems?' It flips the dynamic and shows confidence. Luna: That's a pro move. It also gives you feedback on whether you're on the right track. Lucas: Exactly. So to recap: clarify, assume, calculate, range. Narrate everything. Stay calm. And remember, the interviewer is on your side — they want to see how you think, not catch you in a mistake. Luna: Great advice. I think a lot of listeners will feel more prepared just knowing that framework. Lucas: Good. Next time, we'll talk about how to handle the curveball question that seems completely unrelated to the job. Until then, good luck out there.