Introduction
Brain teasers and estimation questions appear less frequently in investment banking interviews than they once did, but they remain a tool that some interviewers use to test structured thinking under pressure. Unlike technical questions (which have definitive answers), brain teasers have no single correct answer. The interviewer evaluates your process: how you break down an ambiguous problem, what assumptions you make, and whether you arrive at a reasonable estimate.
The Estimation Question Framework
When faced with an estimation question ("How many gas stations are in the United States?" or "What is the annual revenue of the coffee shop downstairs?"), use a structured top-down or bottom-up approach:
Clarify the Question
Make sure you understand what is being asked. "Gas stations" means fueling stations, not including EV charging-only stations? "Revenue" means top-line sales, not profit?
Break Into Components
Decompose the problem into smaller, estimable pieces. For gas stations: US population (~330 million), average people per car (~1.5, so ~220 million cars), average cars per gas station (~1,000-1,500), yielding approximately 150,000-220,000 gas stations.
State Your Assumptions Explicitly
"I'm assuming approximately 220 million registered vehicles and that the average gas station serves about 1,000-1,500 unique vehicles." Making your assumptions transparent is more important than getting them exactly right.
Calculate
Walk through the math out loud. Rounding is fine. The interviewer wants to see your process, not your arithmetic precision.
Sanity Check
Does the answer feel reasonable? "150,000-220,000 gas stations in the US seems about right based on my experience that there's roughly one every few miles in suburban areas."
- Estimation Question (Market Sizing)
An interview question that asks the candidate to estimate a quantity (market size, revenue, number of items) using structured reasoning and stated assumptions rather than memorized data. The interviewer evaluates the process (how you break the problem into components, what assumptions you make, whether you sanity-check the result), not the answer (the specific number). A candidate who arrives at 180,000 gas stations through a clear, logical process scores better than one who guesses 150,000 without showing any work. Estimation questions test the same analytical thinking that investment bankers use daily: making reasonable assumptions under uncertainty, structuring a problem from first principles, and communicating the logic clearly.
Valuation-Specific Brain Teasers
Some brain teasers connect directly to valuation concepts:
"A company generates $50 million in EBITDA and trades at $400 million enterprise value. Is it cheap or expensive?"
The implied multiple is 8x EV/EBITDA. Whether that is "cheap" or "expensive" depends on the industry (sector multiples vary widely), the company's growth rate, and the current market environment. A SaaS company at 8x is cheap; a declining retail company at 8x may be expensive. The answer demonstrates whether you understand that multiples are relative, not absolute.
"If a company's stock price doubles, what happens to its EV/EBITDA multiple?"
The stock price doubling doubles equity value (market cap), which increases enterprise value by the same amount (since debt and cash have not changed). EBITDA has not changed, so EV/EBITDA roughly doubles. The exact answer depends on the relative size of equity versus total EV. This tests understanding of the EV bridge.
"Would you rather have $1 million today or $100,000 per year forever?"
This is a perpetuity question. The present value of $100,000 per year forever is $100,000 / discount rate. At a 10% discount rate, the perpetuity is worth $1 million (equal to the lump sum). At rates below 10%, the perpetuity is worth more. At rates above 10%, the lump sum is better. The answer depends on the discount rate, which the candidate should identify as the key variable.
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