Financial Analysis puzzles, solved step by step
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041A distributor prices at cost plus 25%. A competitor says it earns a 25% gross margin. Who keeps more on every Rs 100 of sales, and what markup would give the distributor a 25% margin?Corporate FP&ACost accounting
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What markup on cost delivers a 25% gross margin?
Show the worked solution
The competitor keeps more: Rs 25 against Rs 20 on every Rs 100 of sales. Cost plus 25% means a price of 1.25 times cost, so on Rs 100 of sales cost is Rs 80 and the margin is 20%. A 25% gross margin needs cost of Rs 75 on a price of Rs 100, which is a markup of 25 over 75, or 33.3%.
Why does the same 25% mean different money?
Think of a vegetable seller who buys tomatoes for Rs 80 a kilo and adds Rs 20. To him, that is 25% on what he paid. To his customer, Rs 20 out of the Rs 100 she paid is 20%. Same Rs 20, two percentages. Markup divides profit by cost; margin divides it by price, and price is always the bigger number, so a margin is always smaller than the markup that produced it. The distributor's 25% markup is a 20% margin; the competitor's 25% margin is a 33.3% markup.
On Rs 100 of sales, pricing at cost plus 25% means cost of Rs 80 and Rs 20 kept, while a 25% gross margin means cost of Rs 75 and Rs 25 kept, a markup of 33.3% on cost. Markup on cost Margin on price Kept per Rs 100 of sales 10% 9.1% Rs 9.1 20% 16.7% Rs 16.7 25% 20.0% Rs 20.0 50% 33.3% Rs 33.3 100% 50.0% Rs 50.0 Margin equals markup divided by one plus markup, so the gap widens as the markup grows: a 100% markup is only a 50% margin. Where does this mix-up cost real money?
In pricing conversations, sales teams often quote markups because the numbers sound larger, while finance teams report margins. If a target says 25% margin and the price list is built at cost plus 25%, every sale falls 5 rupees short per Rs 100, a fifth of the profit the plan assumed. Discounts make it worse: a 10% discount off a cost-plus-25% price leaves a price of Rs 90 on cost of Rs 80, an 11.1% margin, so half the profit per unit is gone. Say the conversion formula out loud whenever someone gives you a percentage of profit, and ask which base it is on.
Where candidates lose it
The trap is answering that both keep the same, because both say 25%. The question is built to see whether you ask: 25% of what?
The second loss is getting the conversion backwards and saying a 25% margin needs a 20% markup. Check with Rs 100 of price: cost Rs 75, profit Rs 25, and 25 over 75 is a third.
What the interviewer asks next
- What margin does a 40% markup give?
- A retailer offers 20% off a product priced at cost plus 50%. What margin is left?
- Why do sales teams often prefer to talk in markups?
042A company sells land with a book value of Rs 40 crore for Rs 100 crore and pays 20% tax on the gain. Walk it through the three statements, and explain why the gain is subtracted in cash from operations.Big FourCorporate FP&A
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What does cash from operations show for this transaction?
Show the worked solution
Net income rises Rs 48 crore, cash rises Rs 88 crore, and the balance sheet balances at plus Rs 48 crore. The gain of Rs 60 crore less Rs 12 crore tax gives net income of Rs 48 crore. Cash from operations starts at 48 and subtracts the Rs 60 crore gain, leaving minus 12; investing shows the full Rs 100 crore. Cash is up Rs 88 crore, land down Rs 40 crore.
Why subtract a gain you actually made?
Think of selling your old scooter for Rs 50,000 when you had it on your books at Rs 20,000. You did receive Rs 50,000 in cash, all of it, on the day of the sale. If your diary records a Rs 30,000 profit under daily earnings and also Rs 50,000 under scooter sold, you have counted Rs 30,000 twice. The cash flow statement puts the full sale proceeds in investing, so the gain sitting inside net income has to be taken out of operations, or part of the sale would be counted twice.
Cash from operations starts at net income of Rs 48 crore and backs out the Rs 60 crore gain, leaving minus Rs 12 crore of tax, while investing carries the full Rs 100 crore of proceeds, so cash rises Rs 88 crore and the balance sheet balances at plus Rs 48 crore. How does each statement move, line by line?
Income statement: a gain on sale of Rs 60 crore, tax of 20% on it, Rs 12 crore, so net income is up Rs 48 crore. Cash flow statement: start from net income of 48, subtract the non-operating gain of 60, and cash from operations is minus 12; investing shows plus 100; cash is up 88. Balance sheet: cash up 88, land down 40, so assets are up 48; retained earnings up 48. The check that matters is that the change in assets equals the change in equity, Rs 48 crore each side.
State the assumption: the tax is paid in cash in the same year. If it were deferred, operations would show zero, a tax liability would sit on the balance sheet and cash would be up the full Rs 100 crore. Say also why the tax stays in operations: accounting rules generally classify income taxes as operating unless they are specifically tied to an investing activity, and practice varies, so confirm the treatment the company uses.
Where candidates lose it
The trap is putting the Rs 100 crore in operations, or putting it in investing and forgetting to back out the gain. The second version leaves cash up Rs 148 crore, and the balance sheet will not balance.
Candidates also put the gain on the cash flow statement as an add-back, the way they treat depreciation. Depreciation is a non-cash expense, so it is added back. A gain is a non-operating income, so it is subtracted. Say which one it is before you pick the sign.
What the interviewer asks next
- What changes if the land is sold for Rs 30 crore, a loss?
- How would the answer change if the tax is deferred to next year?
- Where would the sale of a machine at book value show up?
043A company earns Rs 100 crore with 10 crore shares trading at Rs 200. It borrows Rs 400 crore at 9%, with a 25% tax rate, to buy back 2 crore shares. What happens to EPS, and at what P/E would the buyback break even?Deutsche BankSan Francisco · 2025
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Fewer shares, more interest. Which way does EPS move?
Show the worked solution
EPS falls from Rs 10.00 to Rs 9.125; the buyback breaks even at a P/E of 14.8x. After-tax interest is 400 x 9% x 75% = Rs 27 crore, so net income drops to Rs 73 crore over 8 crore shares. The shares cost 20x earnings, a 5% earnings yield, but the debt costs 6.75% after tax. EPS rises only if the P/E is below 1 / 0.0675 = 14.8x.
What decides whether a buyback raises or lowers EPS?
Think of borrowing at 9% to buy a shop that pays you 5% of its price in profit each year. Your income falls, even though you now own more. Buying your own shares is buying their earnings: it raises EPS only if the earnings yield on the shares, one over the P/E, beats the after-tax cost of the money used. At Rs 200 a share and EPS of Rs 10, the shares yield 5%. The debt costs 9% x (1 - 25%), which is 6.75%. You pay 6.75% to buy a 5% stream, so EPS falls.
Funding the buyback with 6.75% after-tax debt at 20x earnings cuts EPS from Rs 10.00 to Rs 9.125, and post-buyback EPS only beats the old Rs 10 when the shares are bought below 14.8x, the inverse of the after-tax cost of debt. The relationship1/(P/E) the earnings yield on the shares bought back r_d(1-t) the after-tax cost of the debt used to buy them What it says in wordsA debt-funded buyback raises EPS only when the earnings yield on the shares beats the after-tax interest rate.Does a lower EPS mean the buyback destroys value?
Not by itself. EPS is an accounting test, and it ignores what happens to risk. Replacing equity with debt raises the risk borne by every remaining share, so a fall in EPS can sit alongside an unchanged or higher share price if the debt tax shield is worth more than the extra risk. Equally, a rise in EPS at a low P/E is not proof of value created. Say both sides: the EPS answer is Rs 9.125, the breakeven is 14.8x, and the value question turns on whether the shares were bought below what they are worth and on what the extra leverage does to the cost of equity.
Where candidates lose it
The fast wrong answer is that EPS rises because there are fewer shares: Rs 100 crore over 8 crore shares, Rs 12.50. That forgets the interest on the borrowing, which is the whole point of the question.
The second loss is forgetting tax. Interest is tax deductible, so the cost that matters is 6.75%, not 9%. Using the pre-tax rate gives a breakeven P/E of 11.1x and the wrong threshold.
What the interviewer asks next
- What if the buyback were funded with cash earning 4% before tax?
- At what share price would the buyback be exactly EPS-neutral?
- Why might a board do a dilutive buyback anyway?
Asked at Deutsche Bank, Investment Banking, San Francisco, 2025 (Wall Street Oasis):
What happens to EPS if a company issues debt to buyback shares
044Revenue went from Rs 100 crore to Rs 200 crore in five years and management calls it 20% annual growth. What is the true compound annual growth rate? And what is it for yearly growth of 50%, minus 20%, 30%, 10% and 5%?Corporate FP&AEquity research
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Doubling in five years is what compound rate?
Show the worked solution
The true CAGR is 14.9%, and the second series compounds at 12.5%, not the 15% its average suggests. Doubling in five years means (200/100) to the power one-fifth, less one: 14.87%. For the yearly series, multiply the growth factors: 1.5 x 0.8 x 1.3 x 1.1 x 1.05 = 1.8018, whose fifth root gives 12.50%. A simple average ignores both compounding and volatility.
Why is doubling in five years not 20% a year?
Think of a savings account that pays interest on interest. To double your money in five years you need less than 20% a year, because each year's growth is earned on a larger balance. Total growth divided by the number of years ignores compounding, so it always overstates the annual rate for a gain. The rate that compounds 100 to 200 in five years is the fifth root of 2 less one, 14.87%. Compounding at the claimed 20% would have produced 248.8.
Compounding at 14.9% takes revenue from 100 to 200 in five years while the claimed 20% would have reached 249, and yearly growth that averages 15% only takes 100 to 180.2, a compound rate of 12.5%. The relationshipg_i growth in year i product multiply the yearly growth factors, do not add the rates What it says in wordsMultiply the growth factors, take the n-th root, and subtract one.Why does an uneven path lose so much to its average?
A fall hurts more than an equal rise helps, because the rise then starts from a smaller base: 100 up 50% is 150, down 20% is 120, not 130. The gap between the average and the compound rate grows with how much the yearly rates vary; roughly, CAGR is the average less half the variance of the rates. Here the rates have a variance of 0.056, so the shortcut gives 15% less 2.8 points, about 12.2%, close to the exact 12.5%. Use this when a pitch quotes average growth: ask for the start and end values and compute the compound rate yourself.
Where candidates lose it
The trap is dividing the total gain by the years: 100% over five is 20%. It is the number management wants you to repeat, and it overstates growth by about five points a year.
For the uneven series, candidates add the rates and divide by five. Multiply the factors instead, or at least say that volatility drags the compound rate below the average.
What the interviewer asks next
- What is the CAGR if revenue triples in ten years?
- A fund gains 100% then loses 50%. What is its two-year CAGR?
- Why do analysts quote CAGR rather than average growth for revenue?
045A snack pack shrinks from 100 g to 90 g while its price stays at Rs 50. What is the effective price rise per gram?Corporate FP&ACost accounting
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Pick the effective price rise.
Show the worked solution
About 11.1%. Before, Rs 50 buys 100 g, Rs 0.500 a gram. After, Rs 50 buys 90 g, Rs 0.556 a gram. The rise is 100 over 90 less one, which is 10 over 90, or 11.1%. In general a size cut of x at the same price is a price rise of x divided by (1 minus x), always a little more than the cut.
Why is a 10% smaller pack more than a 10% price rise?
Think of sharing the same Rs 50 bill among 10 friends instead of 11. Each pays more, and the increase is measured against the new, smaller headcount. Price per gram is price divided by grams, so cutting the grams by 10% divides the price by 0.9, which raises it by 1/0.9 less one, 11.1%. The percentage fall in grams is measured on 100; the percentage rise in price per gram is measured on what is left, 90.
Rs 50 for 100 g is Rs 0.500 a gram and Rs 50 for 90 g is Rs 0.556 a gram, an 11.1% rise, and the gap between the cut and the rise grows with the cut: 20% smaller is 25% dearer and 25% smaller is 33.3% dearer. The relationshipx the cut in pack size, as a decimal What it says in wordsA size cut of x at a fixed price is a price rise of x over one minus x.How would a finance team use this?
Inflation in raw materials pushes consumer companies to protect a price point that shoppers remember, such as Rs 10 or Rs 50, and adjust grams instead. To compare price changes across products, convert every pack-size change into a price per unit, or a volume decline will be misread as stable pricing. In a revenue bridge, the same rupee sales on fewer grams show up as a price gain, not as flat sales. Say the limitation: price per gram is the right comparison only if quality and the mix of the pack stay the same.
Where candidates lose it
The trap answer is 10%, the size cut itself. It measures the change against the old pack, while the price per gram has to be measured against the new one.
A second wrong answer is 9.1%, which comes from dividing 10 by 110. That is the rule for the opposite case, a pack that grows 10% at the same price, which is a 9.1% price cut.
What the interviewer asks next
- A pack grows from 100 g to 120 g at the same price. What is the price change per gram?
- The pack shrinks to 90 g and the price falls to Rs 48. What is the net price change per gram?
- How would you show this in a price-volume bridge?
046Sales grow by exactly Rs 10 lakh every month. A team forecasts next month's sales as the average of the last three months. By how much does the forecast miss, and in which direction?Corporate FP&ABusiness finance
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The trend is steady at Rs 10 lakh a month. How far off is the three-month-average forecast?
Show the worked solution
It under-forecasts by Rs 20 lakh every month. On a straight-line trend, the average of the last three months equals the middle month, so the average lags the latest month by one month. The forecast is for the following month, one more month ahead. Two months of Rs 10 lakh growth is Rs 20 lakh. For a window of n months, the miss is the monthly growth times (n + 1) / 2.
Why does an average lag behind a trend?
Think of judging how fast a child is growing by averaging her height over the last three birthdays. The average describes her at the middle birthday, not today, and certainly not next year. A moving average describes the middle of its window, so on a rising trend it always sits below the latest value and further below the next one. With months 4, 5 and 6 at 130, 140 and 150, the average is 140, the month 5 figure, while month 7 will be 160.
Sales rise Rs 10 lakh a month while the three-month average forecast runs parallel but always Rs 20 lakh below, because the average sits at the middle month and the forecast is two months ahead of it. The relationshipb the trend: growth per month, Rs 10 lakh n the number of months in the average (n + 1)/2 months between the centre of the window and the month forecast What it says in wordsOn a straight trend, a moving average forecast misses by the monthly growth times half the window plus one.What does that mean for the window you choose?
A longer window smooths noise better but lags more: a 12-month average on the same trend would miss by 10 x 6.5 = Rs 65 lakh. Moving averages trade noise against lag, so they suit flat, noisy series and fail on trending ones. The fix on a trend is to model the trend itself: add the slope back, or use a method that tracks level and slope separately, such as Holt's linear exponential smoothing. Say the limit both ways: if sales are seasonal, a three-month average also mixes high and low months, and if the trend turns, any trend-adjusted method overshoots for a while.
Where candidates lose it
The common answer is Rs 10 lakh: the forecast uses last month's level, so it is one month behind. That forgets that the average sits at the middle of the window, not at the latest month.
The other loss is saying the error is random. On a steady trend it is a bias: the same Rs 20 lakh in the same direction every month, which is exactly what a forecast review should catch.
What the interviewer asks next
- What is the miss for a six-month moving average on the same trend?
- How would you adjust the moving average to remove the bias?
- What happens to the forecast error in the month after the trend stops?
047A vending machine costs Rs 2 lakh. It sells 50 items a day at Rs 30, each costing Rs 18, for 300 days a year, and the site rent is Rs 60,000 a year. It lasts five years with straight-line depreciation and no salvage value, and the tax rate is 25%. At a 14% discount rate, what is its unlevered free cash flow and NPV?Houlihan LokeyNew York · 2026
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What is the yearly unlevered free cash flow?
Show the worked solution
Unlevered free cash flow is Rs 1,00,000 a year and the NPV is about Rs 1,43,308. Sales are Rs 4,50,000, goods Rs 2,70,000 and rent Rs 60,000, so EBITDA is Rs 1,20,000. Less Rs 40,000 of depreciation is EBIT of Rs 80,000; after 25% tax, NOPAT is Rs 60,000. Adding back depreciation gives Rs 1,00,000. Five years of that at 14% is worth Rs 3,43,308, less the Rs 2 lakh machine.
How do you get from sales to unlevered free cash flow?
Think of a tea stall owner counting what she can take home each year: takings, less tea and milk, less rent, less the tax man's share. The stall's old kettle wearing out is a cost on paper, but no cash leaves her purse for it each year. Unlevered free cash flow is the cash the asset throws off before any financing: operating profit after tax, plus non-cash charges, less the capital spending and working capital it needs. Here: sales of Rs 4,50,000 less goods of Rs 2,70,000 and rent of Rs 60,000 is EBITDA of Rs 1,20,000. Depreciation of Rs 40,000 gives EBIT of Rs 80,000, tax takes Rs 20,000, and NOPAT is Rs 60,000.
Rs 4,50,000 of sales becomes Rs 1,20,000 of EBITDA after goods and rent, Rs 60,000 of NOPAT after depreciation and tax, and Rs 1,00,000 of unlevered free cash flow once depreciation is added back, which over five years at 14% gives an NPV of Rs 1,43,308. The relationshipEBIT(1 - t) NOPAT: operating profit after tax, ignoring interest D&A depreciation, added back because it is not cash capex, change in NWC zero here after the initial purchase What it says in wordsTax the operating profit as if there were no debt, add back non-cash charges, and take off the investment the asset needs.Year Cash flow, Rs Discount factor at 14% Present value, Rs 0 (2,00,000) 1.0000 (2,00,000) 1 1,00,000 0.8772 87,719 2 1,00,000 0.7695 76,947 3 1,00,000 0.6750 67,497 4 1,00,000 0.5921 59,208 5 1,00,000 0.5194 51,937 NPV 1,43,308 Five years of Rs 1,00,000 discounted at 14% are worth Rs 3,43,308, so after the Rs 2,00,000 purchase the NPV is Rs 1,43,308 and the internal rate of return is about 41%. Why does depreciation matter only through tax?
Depreciation is subtracted to reach EBIT and added back to reach cash flow, so on its own it washes out. Its only cash effect is the tax it saves: Rs 40,000 of depreciation at 25% cuts tax by Rs 10,000 a year. That is why taxing EBITDA directly is wrong: it would give Rs 90,000 a year and lose the shield. The answer leans on assumptions you should say out loud: no working capital for stock in the machine, no repairs, no salvage value, a steady 50 sales a day, and a 14% rate that reflects the risk of the location. The NPV is positive by a wide margin, so the decision is most sensitive to daily volume, the one number nobody can check in advance.
Where candidates lose it
Candidates stop at EBITDA, or tax the EBITDA, and call it free cash flow. Unlevered free cash flow taxes EBIT, not EBITDA, and then adds back depreciation; skipping the order loses the tax shield or double counts it.
The second loss is forgetting the Rs 2 lakh outlay at year 0, or depreciating it and also subtracting it as capex in every year. Spend it once, at the start, and let depreciation work only through tax.
What the interviewer asks next
- How many items a day does the machine need to sell to break even on NPV?
- If you financed the machine with a loan at 10%, would the unlevered free cash flow change?
- How would working capital for stock in the machine change the answer?
Asked at Houlihan Lokey, Investment Banking, New York, 2026 (Wall Street Oasis):
Question about valuing a vending machine (use a DCF and explain how to get unlevered free cash flows)
048Quickly, without a calculator: what is 1/7 as a decimal, what is 5/7 of 910, and what is 3/7 as a percentage to two decimal places?Private equityConsulting-style case
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Which is 3/7 to two decimals?
Show the worked solution
1/7 is 0.142857 repeating, 5/7 of 910 is 650, and 3/7 is 42.86%. 910 divides cleanly by 7 to give 130, and five of those is 650. For any seventh, the six digits 142857 repeat in the same order; only the starting digit changes. 3/7 is about 0.43, so it starts at the 4: 0.428571, or 42.86%.
Why should sevenths be memorable when they look messy?
Think of a clock face with six numbers on it instead of twelve. Whatever hour you start from, you read the same numbers in the same order. Sevenths work like that: every k/7 is the cycle 1, 4, 2, 8, 5, 7 read round the ring from a different starting digit. You only need to learn one string, 142857, and a way to pick the start: k/7 is roughly k x 0.14, so 2/7 starts at 2 (0.285714), 3/7 at 4 (0.428571) and 6/7 at 8 (0.857142).
The six digits 142857 repeat in every seventh, so 3/7 reads 0.428571 starting from the 4 and is 42.86%, while 5/7 of 910 is simply 910 divided by 7, which is 130, times 5, or 650. When should you divide first and when should you use the decimal?
For 5/7 of 910, check whether 7 divides 910: 7 x 130 is 910, so divide first and multiply second, and the answer is a clean 650. When the number you are taking a fraction of is a multiple of the denominator, divide first; reach for the decimal only when it is not. For 5/7 of 1,000, there is no clean division, so use the cycle: 5/7 starts at the 7, 0.714285, and the answer is about 714.3. A check that works on both: 5/7 is a little over 70%, and 70% of 910 is 637, so 650 sits in the right place.
Interviewers use sevenths because the decimals look random and catch people who have only learned halves, quarters and eighths. The cycle gives you six decimal places in a second, which is more precision than you will ever need to say out loud.
Where candidates lose it
Candidates try long division for 3/7, get 0.43 after a pause, and then guess the second decimal. The cycle gives the full 0.428571 at once, so 42.86% is not a guess.
For 5/7 of 910, the slip is converting 5/7 to 0.714 first and multiplying, which invites a rounding error. Notice that 910 is a multiple of 7 and the answer is exact.
What the interviewer asks next
- What is 4/7 as a percentage to two decimals?
- What is 6/7 of 1,400?
- Why do sevenths repeat in a six-digit cycle?
049A table shows segment revenue for two years: A Rs 400 crore to Rs 460 crore, B Rs 250 crore to Rs 240 crore, C Rs 350 crore to Rs 420 crore. Which segment's share of total revenue rose the most, and by how many percentage points?BarclaysNew York · 2026
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Which segment gained the most share?
Show the worked solution
Segment C, up 2.5 percentage points, from 35.0% to 37.5%. Total revenue rises from Rs 1,000 crore to Rs 1,120 crore, 12% growth. C grew 20%, and 420 of 1,120 is 37.5%. A grew 15% but its 460 of 1,120 is 41.1%, only 1.1 points above 40.0%. B shrank 4% and lost 3.6 points, falling to 21.4%.
Why is growth not the same as gaining share?
Think of a household where every earner got a raise this year. Whose share of the family income went up most? Not the one with the biggest raise in rupees, and not necessarily the one with a big raise at all, but the one whose raise beat the household's overall rise by the widest margin. A segment gains share only by growing faster than the total, so the first number to compute is total growth, here 12%. A grew 15%, three points faster than the total; C grew 20%, eight points faster; B shrank.
Total revenue grows 12% from Rs 1,000 crore to Rs 1,120 crore, so segment C, growing 20%, lifts its share from 35.0% to 37.5%, while A grows 15% but gains only 1.1 points and B loses 3.6 points. The relationships0 the segment's share in year one g the segment's own growth G growth of the total, 12% What it says in wordsThe change in share is the old share times how far the segment outgrew the total, scaled down by the total's growth.How do you answer this fast in a timed test?
Sum each column first: 1,000 and 1,120. Compare every segment's growth with 12%, and only A and C can have gained. Then use the formula on those two: C is 0.35 x 8/112, which is 2.5 points; A is 0.40 x 3/112, about 1.07. Shares always add to 100%, so the gains and losses must net to zero, which gives a free check: 2.50 + 1.07 - 3.57 = 0. Watch the units in the answer options: C's share rose 2.5 percentage points, which is a 7.1% rise in its share. Timed numerical tests often offer both, and only one matches the question's wording.
Where candidates lose it
The trap is picking A because it added Rs 60 crore on the largest base, or because 15% sounds strong. Share depends on growth relative to the total, and A beat the total by only three points.
The second loss is mixing percentage points and per cent. A share moving from 35.0% to 37.5% is up 2.5 points or about 7.1%. Read which one the question asks for before you choose.
What the interviewer asks next
- What growth would segment B have needed to hold its 25% share?
- If total revenue had grown 20%, which segments would have gained share?
- Why might a segment that loses share still be the most valuable one?
Asked at Barclays, Investment Banking, New York, 2026 (Wall Street Oasis):
The numerical section involved interpreting tables and charts quickly
050Estimate how many ATMs a city of one crore people needs.Rothschild & CoNew York · 2026
Try it first
Which load should you size the number of machines to?
Show the worked solution
About 2,520 ATMs, on stated assumptions. Of one crore people, 70 lakh are adults and 60% of them, 42 lakh, use ATMs about three times a month: 4.2 lakh withdrawals a day. If 12% fall in the busiest hour, that is 50,400 an hour. A machine handles 30 an hour at two minutes each; plan for two-thirds busy, 20 an hour, and you need about 2,520.
Where do you start, demand or supply?
Think of a canteen deciding how many counters to open. It does not divide the day's meals by 24 hours; it counts the lunch rush and opens enough counters for that. Size a service network to its peak load, so the estimate runs from people to withdrawals to the busiest hour, and only then to machines. Start with demand: 70% of one crore are adults, 70 lakh; assume 60% of them use ATMs for cash, 42 lakh, and that each withdraws three times a month. That is 1.26 crore withdrawals a month, or 4.2 lakh a day.
One crore people make about 4.2 lakh ATM withdrawals a day, of which 50,400 fall in the busiest hour, and at 20 withdrawals per machine an hour the city needs about 2,520 ATMs, nearly three times the 875 that a 24-hour average would suggest. How much does the peak assumption change the answer, and how do you check it?
Machines stand idle at 3 a.m. and have queues at 6 p.m. If you spread 4.2 lakh withdrawals evenly over 24 hours, you would size for 17,500 an hour and buy 875 machines. The peak-hour share is the assumption that moves the answer most: at 12% of the day in one hour, the city needs nearly three times what the average implies. The same logic explains the planning margin: a machine busy 100% of the time has a queue that never clears, so plan for two-thirds use. Then sanity check the result: 2,520 machines for one crore people is about 25 per lakh, a ratio you can compare with the published ATMs-per-lakh figure for the city, which you should look up rather than quote from memory.
Say what you left out. Salary days bring a bigger rush at the start of the month; digital payments are shrinking cash use, so the user share and the withdrawals per month are both falling; and machines sit where people work and shop, so a city with a dense business district needs more than population alone suggests.
Where candidates lose it
The common slip is sizing to the average: daily withdrawals divided by 24 hours and by a machine's capacity. It gives a number about a third too small and misses the point the interviewer is testing, that networks are built for the rush.
The second loss is reciting a ratio you half remember instead of building the number. Build it first, then offer the per-lakh ratio as a check you would verify.
What the interviewer asks next
- How would the answer change if half of withdrawals moved to digital payments?
- How many ATMs would you put in a business district of 5 lakh daytime workers?
- How would a bank decide whether one more ATM in an area pays for itself?
Asked at Rothschild & Co, Generalist, New York, 2026 (Wall Street Oasis):
1st round all technical focused mainly on DCF and Eq Val and Enterprise Value questions, mental math, and some market sizing
