Real Interview Bank: Actual Guesstimate Questions from MBB, Big-4, Tech and Banking
After using The 25-Point Grading Rubric to score structure, assumptions, maths, sanity-checking and communication, the next question is simple: what should you practise on? This bank answers that with real guesstimate prompts reported from MBB India, Big-4 consulting, tech product management and Indian banking. The big shift is that modern Indian guesstimates are typically live business-sizing problems - EV adoption, UPI usage, D2C beauty, GCC growth - not just abstract Fermi puzzles.
- Real Indian interview guesstimates increasingly test live business sizing, not only fun abstract estimates.
- MBB India prompts from McKinsey, BCG and Bain cover diagnostics, electric scooters, D2C beauty, credit cards, GCCs and highway fuel.
- Big-4 prompts from Deloitte, EY, KPMG and PwC focus on practical markets such as laptops, demat accounts, hotel banquets and wellness apps.
- Tech and PM prompts from Google, Meta India, Amazon, JioStar, Flipkart and PhonePe test platform usage, transaction behaviour and GMV thinking.
- Banking prompts from HDFC, Kotak, Axis and ICICI test lending, deposits, cards and MSME working-capital markets.
- Follow-ups usually test sensitivity, self-criticism, research instinct, projection, composure, transferability, segmentation and humility.
At a glance, the real interview bank clusters into five domains. Each domain has a different business lens, but the scoring logic remains the same: clarify scope, build a tree, use defensible assumptions, calculate cleanly and sanity-check the answer.
Why This Bank Matters in Indian Interviews
A Fermi estimate is a rough, assumption-led estimate made when exact data is unavailable, such as estimating the number of grains of rice eaten in India daily. These classic puzzles still appear, mainly as warm-ups, but the interview pattern has moved toward live business questions.
MBB means McKinsey, BCG and Bain. Big-4 refers here to Deloitte, EY, KPMG and PwC consulting. PM means product management, where questions often test product usage, transactions and growth. FY means financial year, such as FY24 or FY25.
Modern Indian guesstimates usually ask you to size a real business activity - for example EV sales, UPI usage, D2C beauty or GCC demand - so sector intuition gives you a 30-second head-start.
Live Business Sizing vs Classic Fermi Warm-ups
The source bank separates modern business-sizing questions from classic fun Fermi questions. Both need structured estimation, but they reward slightly different instincts: business prompts reward market logic and segment understanding, while classic prompts reward physical reasoning and unit control.
MBB India Question Bank
The MBB India questions reported from McKinsey, BCG and Bain are strongly business-facing. They ask candidates to think like someone sizing a market for a client, not like someone solving a trivia puzzle.
D2C means direct-to-consumer, where a brand sells directly to consumers rather than only through intermediaries. GCC means Global Capability Centre, a corporate centre that performs technology, operations, analytics or other capability functions for a global organisation. These acronyms matter because interviewers expect candidates to understand the business context before building the estimation tree.
Big-4 Consulting Question Bank
The Big-4 questions are practical and commercially grounded. They often sit closer to implementation, operations and market entry style thinking, where the candidate must size real demand rather than only produce a neat mathematical model.
A demat account is an account used to hold securities in electronic form. The EY demat-account question is a good example of a prompt that sounds simple but requires the candidate to think through new account openings, investor adoption and validation sources.
Tech and PM Question Bank
Tech and product management interviews use guesstimates to test whether candidates understand user behaviour at platform scale. These questions often require frequency, active usage and transaction intensity, not just population counts.
GMV means Gross Merchandise Value, the total value of goods sold through a platform before deductions. UPI means Unified Payments Interface, India's real-time payments system. A PM interviewer is typically looking for a usable structure, sensitivity to behaviour and the ability to defend assumptions under follow-up questioning.
Indian Banking Question Bank
Banking guesstimates test comfort with financial products and customer segments. The candidate must usually distinguish accounts, active usage, balances, spend, loans and market value.
FD means fixed deposit. MSME means micro, small and medium enterprises. In banking prompts, a strong answer usually separates volume from value: for example, number of accounts is not the same as balances, and number of cards is not the same as annual card spend.
Classic Fermi Warm-ups Still Asked
The source bank still includes fun Fermi prompts, mainly as warm-ups. They are less business-specific, but they remain useful because they expose weak unit discipline, missing scope and lack of sanity-checking.
Calibration Anchors That Prevent 10x Errors
The source notes that strong students can get the structure right but still land 10x away because their base intuition for Indian scale is weak. Calibration drills train the ability to feel the right magnitude before doing a full guesstimate.
Do 10 calibration drills per day for 3 weeks before interviews. The goal is to feel the right order of magnitude before checking the answer key.
Follow-up Question Bank
Real interviews rarely stop at the first number. The differentiation happens after the answer, when the interviewer tests whether the candidate can critique, adapt and defend the estimate.
Reusable Answer Shape for Any Real Interview Bank Prompt
The question bank is broad, but the answer shape is reusable. The same structure can handle a McKinsey diagnostic-labs prompt, a Google searches prompt or an Axis credit-card-spend prompt, with only the input anchors changing.
Scope first, tree second, assumptions third, calculation fourth, sanity-check fifth, follow-up response sixth.
Worked Example: BCG Electric Scooters in FY28
Use this as a worked approach, not as a memorised numerical answer. The source gives the real prompt - "How many electric scooters will India sell in FY28?" - reported from BCG IIM-B, FY24.
The key move is to treat FY28 as a projection problem. A candidate who only multiplies current-looking numbers may miss the strategic part of the question: which assumptions drive adoption, and which one would change the estimate most?
How to Practise This Bank
Do not solve the list by memorising final answers. The source's grading advice is to score yourself before comparing your number to anyone else's, because the learning comes from diagnosing structure, assumptions, maths, sanity-checking and communication.
After every attempt, grade the answer first. A structured 22/25 answer that is wrong by 30 percent is more useful than a 12/25 answer that happens to land near the right number.
Conclusion
The Real Interview Bank shows the practical direction of Indian guesstimates: interviewers now use market, product, banking and platform questions to test structured business judgement. Practise the domains, rehearse the follow-up moves and use calibration anchors so your final answer is not just structured, but also plausible.
The most frequent error is starting calculations in minute 1 without clarifying scope, approach and tree. It costs points because the interviewer cannot see your structure, and it often leads to weak assumptions, unit errors and no sanity-check.