Latest / Interview Prep with Fexingo: Behavioral Questions, Case Studies, and Hiring Manager Insights / How to Answer a Brainteaser Interview Question
Transcript
- Lucas: So today we are talking about brainteasers. You know, those oddball questions that feel less like an interview and more like a puzzle from a cocktail napkin. Luna: Right, the classic: 'Why are manhole covers round?' or 'How many golf balls fit in a 747?' Lucas: Exactly. And if you're preparing for a consulting, tech, or finance interview, you've probably seen these come up. The thing is, most candidates freeze because they think there's a single correct answer. Luna: But there isn't, is there? It's more about the process. Lucas: Right. Interviewers aren't looking for the exact number of golf balls. They want to see how you think under pressure, how you structure a problem, and whether you can communicate your reasoning clearly. So let's break down a framework that works for any brainteaser. Luna: Okay, lay it on me. Lucas: Step one: clarify the constraints. Most brainteasers are deliberately vague. So you ask: 'What kind of 747? A passenger plane? Cargo? Which model? And are we filling the entire interior volume, or just the cabin?' Luna: That already shows you're not jumping to assumptions. Lucas: Exactly. The interviewer will often say, 'Assume a standard passenger 747, and fill everything including cargo holds.' Now you have a boundary. Step two: structure your approach. Break it into pieces: length of the fuselage, width, height. Roughly estimate the total volume. Luna: And then account for the fact that spheres don't pack perfectly. Lucas: Right, there's about a 74% packing efficiency for spheres in a random close pack. So you'd multiply your volume by 0.74. Step three: do the math out loud. You don't need to be exact — you just need a reasonable chain of logic. Luna: And if you mess up a number, it's fine, as long as you correct yourself? Lucas: Absolutely. In fact, correcting yourself shows composure. I once saw a candidate in a McKinsey interview start estimating the number of gas stations in the US. He said 150,000, then paused and said, 'Actually, that's too high. There are about 100,000.' He got the offer. Luna: So the key is to keep talking. Silence is the enemy. Lucas: Exactly. Even if you're stuck, narrate: 'I'm thinking about how to approach this. Let me start with the size of a standard round manhole cover...' That buys you time and shows engagement. Luna: Alright, let's play out the manhole cover question. Why are they round? Lucas: Classic. So first, clarify: 'Do you mean why are they circular rather than square or rectangular?' The interviewer says yes. Then you list reasons. One: a round cover can't fall through its own hole because the diameter is constant. A square cover can be rotated to fall through along the diagonal. Luna: Safety first. Lucas: Two: round covers are easier to manufacture and roll to the side. Three: they don't need to be aligned perfectly to fit back in place. Four: the circular shape distributes stress evenly, which is better for traffic loads. Luna: That's actually a good answer. And you've shown you can think of multiple angles. Lucas: Right. The interviewer might then ask, 'Okay, but what if we made them triangular?' And then you have to think on your feet again. But the framework stays the same: clarify, structure, calculate or reason, and communicate. Luna: Now, what about the criticism that brainteasers are kind of outdated? I know Google banned them a few years ago because they didn't predict job performance. Lucas: That's a fair point. Google did move away from brainteasers around 2013 after internal data showed they weren't predictive. But many firms still use them, especially in consulting, because they test quick thinking and comfort with ambiguity. And they're still used in quant roles. Luna: So it's worth being prepared, even if you hope you don't get one. Lucas: Exactly. And honestly, the preparation itself improves your structured thinking for case interviews too. It's not wasted time. Luna: One thing I always wonder: how do you practice these without a partner? Lucas: You can practice alone. Pick an object in the room — a chair, a lamp — and estimate its volume or weight. Or Google 'brainteaser questions' and talk through your answer out loud. Record yourself and listen for moments where you went silent. Luna: That's a good tip. Also, timing yourself helps. You don't want to ramble for ten minutes. Lucas: Right. Aim for two to three minutes total. Enough to show your thinking, not so long that you lose them. Luna: And if you completely blank? What's your emergency move? Lucas: Ask a question. Say, 'I want to make sure I'm thinking about this correctly — could you clarify whether we're including the cargo hold?' That re-engages the interviewer and gives you a few seconds to regroup. Luna: Good. Or even just say, 'That's an interesting question. Let me think through it step by step.' That's perfectly acceptable. Lucas: Absolutely. And here's something we haven't mentioned: the interviewer might actually be testing your ability to ask for clarification — that's a skill on the job. So don't be afraid to ask. Luna: Alright, let's wrap with a quick example. You're asked: 'How many piano tuners are in Chicago?' Walk me through it. Lucas: Sure. Clarify: do you mean professional piano tuners, or anyone who tunes pianos? Assume professionals. Then structure: estimate the number of households in Chicago, say three million. Assume one in twenty has a piano, so 150,000 pianos. A piano needs tuning once a year, and a tuner can do about four per day, 250 days a year, so 1,000 per year per tuner. That gives you 150 tuners. Luna: And if they ask how you got the three million households? Lucas: I'd say Chicago's population is about 2.7 million, average household size 2.5, so roughly one million households. Then scale. The point is, the numbers don't have to be perfect — the logic chain does. Luna: And that's the whole game, isn't it? Show your work. Lucas: Exactly. And if you can do that with confidence, you'll stand out from most candidates who freeze. Luna: Quick honest thing — a handful of listeners chip in monthly through buy me a coffee dot com slash fexingo, and that's literally what funds making this many of these episodes. We don't run ads, so it's a listener-supported thing. Lucas: Yeah, if you've gotten value from the show — maybe a job offer or just a better interview strategy — that's the way to keep it going. No pressure, but it helps us keep the lights on. Luna: And we really appreciate those of you who do. Alright, back to brainteasers — one last tip: practice with a friend who can throw you curveballs. That's the best simulation. Lucas: Totally. And if you're prepping for a specific firm, check Glassdoor for recent brainteasers they've asked. Some patterns emerge. But the framework works for any of them. Luna: Great episode. Next time we'll tackle the 'tell me about a time you influenced someone without authority' question. Lucas: Looking forward to it. Thanks for listening.