Financial Analysis puzzles, solved step by step
- Puzzles
- 100
- Traced to a firm
- 47
- Topics
- 13
- Hard
- 30
021You invest Rs 10,000 in a fund when its NAV is Rs 100, and another Rs 10,000 when the NAV is Rs 50. What is your average cost per unit, and why is it not Rs 75?Corporate FP&ABusiness finance
Try it first
What is your average cost per unit?
Show the worked solution
About Rs 66.67 a unit, not Rs 75. The first Rs 10,000 buys 100 units at Rs 100 and the second buys 200 units at Rs 50, so Rs 20,000 buys 300 units. Rs 75 is the average of the two prices, which would be your cost only if you had bought equal numbers of units. Equal rupee amounts buy more units when the price is low, so the average cost is the harmonic mean of the prices.
Why does the cheap purchase count for more?
Think of filling your scooter with Rs 500 of petrol every week. In a week when petrol is cheap, Rs 500 buys more litres; when it is dear, fewer. At the end of the month the litres you own lean towards the cheap weeks. A fixed rupee amount buys more units when the price is low, so the low price carries more weight in your average cost than the high one. Here Rs 10,000 buys 100 units at Rs 100 but 200 units at Rs 50, so the Rs 50 price carries two thirds of the weight.
The relationshiptotal spent Rs 20,000 across both purchases total units 100 units at NAV 100 plus 200 at NAV 50 2 / (1/100 + 1/50) the harmonic mean of the two prices What it says in wordsAverage cost is money spent over units bought, which for equal rupee amounts is the harmonic mean of the prices.Rs 10,000 buys 100 units at a NAV of 100 and 200 units at a NAV of 50, so Rs 20,000 buys 300 units at an average cost of Rs 66.67. That harmonic mean sits below both the geometric mean of 70.7 and the simple average price of 75. When is Rs 75 the right answer?
When you buy equal numbers of units rather than equal rupee amounts. Buy 100 units at Rs 100 and 100 units at Rs 50 and you spend Rs 15,000 on 200 units, which is exactly Rs 75 a unit. So the right average depends on what you held fixed: units fixed gives the simple average of prices, money fixed gives the harmonic mean. This is the arithmetic behind the idea of rupee cost averagingInvesting the same rupee amount at regular intervals, so that more units are bought when prices are low and fewer when they are high..
What you hold fixed Units bought Spent, Rs Average cost, Rs Rs 10,000 each time 300 20,000 66.67 100 units each time 200 15,000 75.00 The same two prices give two different average costs, depending on whether the rupee amount or the number of units was held constant. Does the lower average cost mean you made money?
No, and saying so is the mark of a careful answer. A lower average cost is arithmetic about what you paid, not a return. If the NAV stays at Rs 50, your 300 units are worth Rs 15,000 against Rs 20,000 invested, a 25% loss. Your break-even NAV is Rs 66.67, not Rs 75, which is the useful fact. The effect also needs prices to vary: at a constant price every average is the same.
Where candidates lose it
The common loss is answering Rs 75 by averaging the two prices. It ignores that the purchases bought different numbers of units, and it is the same slip people make when they average two speeds for a journey.
The second loss is going too far the other way and describing the lower average cost as a gain. Give Rs 66.67, say break-even is at that NAV, and stop short of claiming anything about returns.
What the interviewer asks next
- You invest Rs 10,000 at NAV 100, then 50, then 100 again. What is your average cost?
- What NAV do you need to break even on the two purchases?
- Why is the harmonic mean of two different positive numbers always below their simple average?
024Four people must cross a narrow bridge at night. They take 1, 2, 5 and 10 minutes to cross. At most two can cross at once, they have one torch, and anyone crossing needs it, so a pair moves at the slower person's pace. What is the fastest everyone can get across?Belvedere TradingChicago · 2021
Try it first
What is the fastest total time?
Show the worked solution
17 minutes. 1 and 2 cross (2 minutes) and 1 brings the torch back (1). Then 5 and 10 cross together (10), and 2 brings the torch back (2). Finally 1 and 2 cross again (2). The obvious plan, where the 1-minute person escorts everyone, takes 19 minutes because the two slowest walkers cost 15 minutes on separate trips but only 10 together.
Why does the obvious plan lose two minutes?
The escort plan sounds efficient: the fastest person walks each one across and runs back with the torch. It costs 2, 1, 5, 1 and 10, which is 19 minutes. The waste is that the 5 and the 10 cross on separate trips, so you pay both their times, 15 minutes, when one shared trip would cost only 10. Think of two slow friends who will hold up any group they walk with; the cheapest thing is to let them hold up the same group, once.
Sending 5 and 10 across together costs 10 minutes instead of 15, and the price is one extra return by the 2-minute walker. The schedule totals 17 minutes against 19 for the plan in which the fastest walker escorts everyone. How do you make sure the torch is on the right side?
If 5 and 10 cross first, one of them has to bring the torch back, which costs at least 5 more minutes. So before the slow pair goes, a fast walker must already be waiting on the far side to carry the torch back. That is why 1 and 2 go first and 1 returns: it parks the 2 on the far side. After the slow pair crosses, the 2 brings the torch back, and the fast pair finishes together.
How do you show 17 cannot be beaten?
There must be three forward trips and two returns. The 10 must cross on some forward trip, costing 10. If the 5 crossed on a different forward trip, the forward trips alone would cost at least 10 + 5 + 2, which is 17, and the two returns add at least 2 more, so 5 and 10 must share a trip. The slow pair cannot go first, or one of them walks the torch back. So 1 and 2 go first, costing 2, and one of them returns. After the slow pair crosses, the only fast walker on the far side is whichever of 1 and 2 stayed, so the two returns cost 1 + 2 between them, and the last trip, 1 and 2, costs 2. That gives at least 10 + 2 + 2 + 1 + 2 = 17. A brute-force search over every schedule confirms 17.
The relationshipa the fastest walker, 1 minute b the second fastest, 2 minutes c the second slowest, 5 minutes What it says in wordsSending the slow pair together costs the 2 an extra return; escorting costs the 5 an extra trip. Pick whichever is cheaper.Where candidates lose it
The common loss is announcing 19 minutes with confidence, because the escort plan feels optimal: the fastest person does all the running. The interviewer is waiting for you to notice that the slowest people's times are what you are really paying.
The second loss is finding 17 by trial and error and then having no reason it is the minimum. Have the one-line argument ready: 5 and 10 must cross together, and someone fast must be waiting to bring the torch back.
What the interviewer asks next
- If the times were 1, 4, 5 and 10, which plan would be faster?
- Add a fifth person who takes 12 minutes. What is the fastest crossing now?
- Where in a project plan do you see the same idea of grouping the slowest tasks?
Asked at Belvedere Trading, Trading, Chicago, 2021 (Wall Street Oasis):
crossing the bridge in the shortest amount of time with one flashlight brainteaser
025A supermarket has annual cost of goods sold of Rs 3,650 crore. It pays suppliers in 45 days, holds 20 days of stock, and is paid in cash at the till. If its sales fall 10%, how much cash leaves the business through working capital?Corporate FP&ATreasury
Try it first
Sales fall 10% with payment and stock days unchanged. What happens to cash from working capital?
Show the worked solution
About Rs 25 crore of cash leaves. Cost of goods sold is Rs 10 crore a day, so payables are 45 days, Rs 450 crore, and stock is 20 days, Rs 200 crore. With no receivables, net working capital is minus Rs 250 crore: suppliers fund the business. A 10% fall cuts daily cost to Rs 9 crore, payables to Rs 405 crore and stock to Rs 180 crore, so net working capital rises to minus Rs 225 crore. That Rs 25 crore is cash consumed.
How can a business be funded by its suppliers?
Think of a school canteen where parents pay for the term in advance and the canteen pays its vegetable seller at the end of each month. The canteen holds other people's money for weeks. A supermarket sells for cash at the till, keeps stock for 20 days and pays suppliers after 45, so it collects from customers about 25 days before it pays for the goods. Its net working capital is negative: suppliers are lending it money, free of interest, all year.
The relationship10 cost of goods sold per day, Rs 3,650 crore over 365 20 days of stock held 45 days taken to pay suppliers What it says in wordsNet working capital is stock less payables when customers pay at the till; here suppliers fund Rs 250 crore.Before the fall, payables of Rs 450 crore fund stock of Rs 200 crore, leaving net working capital of minus Rs 250 crore. After a 10% fall, payables of Rs 405 crore and stock of Rs 180 crore leave minus Rs 225 crore, so Rs 25 crore of cash has left the business. Why does shrinking cost this business cash?
Run it as two movements. Stock falls by Rs 20 crore, which frees cash, but supplier credit falls by Rs 45 crore, which the supermarket has to pay out, so the net is Rs 25 crore out. Each day of lower sales means paying suppliers for last month's larger purchases while this month's till receipts are smaller. The mirror image is why such businesses love growth: a 10% rise in sales would release about Rs 25 crore.
What makes the real number worse?
The answer assumes the days stay fixed, and in a downturn they often do not. Suppliers who see sales fall may shorten credit; if payable days drop from 45 to 40, payables fall to Rs 360 crore and the cash outflow grows to about Rs 70 crore. On top of the working capital effect, lower sales also cut profit. Say both, then name the lesson a lender draws: a business funded by its suppliers can look cash-rich while it grows and turn cash-hungry quickly when it shrinks.
Where candidates lose it
The common loss is saying cash comes in, because less stock is needed. That counts only the asset side and forgets that supplier credit shrinks faster, since payables are more than twice the size of stock.
The second loss is saying nothing changes because the days are unchanged. Days are ratios; the rupee balances scale with sales, and the cash moves with the rupees.
What the interviewer asks next
- If sales grew 10% instead, how much cash would working capital release?
- How would the answer change if 20% of sales were on credit with 30-day terms?
- Why might a supermarket's suppliers accept 45-day terms?
027A product sells at a 30% contribution margin. You raise the price by 5% and lose 8% of your volume. Is total contribution better or worse than before, and by how much?Corporate FP&ACost accounting
Try it first
Gut call: you gained 5% on price and lost 8% on volume. Where does total contribution land?
Show the worked solution
Better, by about 7.3%. Take a price of 100 with variable cost 70, so each unit contributes 30. After the rise the price is 105 and each unit contributes 35. Selling 92 units instead of 100 gives 92 x 35 = 3,220 against 3,000 before. Volume could fall as far as 14.3% before the price rise stopped paying.
Why does 5% on price beat 8% on volume?
Picture a tea stall that sells a cup for 10 rupees with 7 rupees of milk, leaves and sugar in it. Raise the price to 10.50 and the stall's profit per cup goes from 3 to 3.50, a sixth more. A price rise falls straight to contribution, so its effect is measured against the margin, not against the price. The volume loss, by contrast, removes whole cups and their contribution at the same rate as the lost units, 8%.
Raising price from 100 to 105 lifts contribution per unit from 30 to 35, a 16.7% gain, so 92 units at 35 earn 3,220 against 3,000 for 100 units at 30, and volume would need to fall 14.3% to erase the gain. How much volume could you lose before the price rise hurts?
Set new contribution equal to old: units times 35 must equal 100 times 30, so units can fall to 3,000 over 35, which is 85.7. The breakeven volume loss for a price rise is the price change divided by the new margin: 5 over 35, or 14.3%. That is why thin-margin businesses gain so much from price and lose so much from discounts: at a 30% margin, a 5% discount needs volume to rise by 5 over 25, a full 20%, just to stand still.
The relationshipDelta p the price change as a share of the old price, 5% m the contribution margin before the change, 30% What it says in wordsVolume can shrink by the price change divided by the new margin before the rise stops paying.Say the limit too. The sum treats variable cost per unit as fixed and ignores any fixed costs that could be cut when volume falls, and it says nothing about customers who leave and do not come back next year.
Where candidates lose it
The usual loss is adding the two percentages: plus 5 and minus 8 is minus 3, so the move looks bad. That treats the price change as if it acted on revenue, when it lands entirely on the contribution slice.
The second loss is working in revenue instead of contribution. Revenue does fall slightly, 105 x 92 is 9,660 against 10,000, and a candidate who stops there gets the answer backwards.
What the interviewer asks next
- At the same 30% margin, how much must volume rise to justify a 10% price cut?
- How does the answer change if the margin is 70%, as in software?
- Which fixed costs would you look at if volume did fall 8%?
030A company's net debt is 3x EBITDA and its cost of debt is 10%. What is its EBITDA interest cover? What does cover become if leverage rises to 5x and the rate to 12%?Rating agenciesBank credit
Try it first
Leverage rises from 3x to 5x and the rate from 10% to 12%. What happens to cover?
Show the worked solution
Cover is 3.3x, falling to 1.7x. Take EBITDA of 100. Net debt of 300 at 10% costs 30 of interest, so EBITDA covers it 3.33 times. At 5x and 12%, net debt is 500 and interest is 60, so cover is 1.67x. Cover is one over leverage times the rate, and 0.30 doubling to 0.60 halves it.
Why is there no need for an actual EBITDA figure?
Think of a household whose loan EMIs are some multiple of monthly salary. Whether the salary is 50,000 or 5 lakh, the share of salary that goes on interest depends only on how many months of salary it borrowed and at what rate. Interest cover is EBITDA over interest, and interest is leverage times EBITDA times the rate, so EBITDA cancels and cover is one over leverage times the rate. Pick EBITDA of 100 only to make the arithmetic visible.
The relationshipL net debt as a multiple of EBITDA r the average cost of debt What it says in wordsInterest cover is the reciprocal of leverage multiplied by the interest rate.With EBITDA of 100, net debt of 300 at 10% costs 30 of interest and gives cover of 3.3x, while net debt of 500 at 12% costs 60 and gives cover of 1.7x, so the two moves together cut cover exactly in half. Why do leverage and rates tend to move together, and what does 1.7x mean?
A lender charges more to a borrower who owes more, so the second scenario is not a coincidence; it is how a stretched balance sheet usually looks. Because leverage and rate multiply, a company that adds debt while rates rise loses cover much faster than either change alone suggests. Cover of 1.7x also flatters the position: EBITDA is before tax, capex and working capital, so once maintenance capex is paid the cash left to service interest can be well under 1.7 times the bill. Say that limitation; credit analysts look at cover after capex for exactly this reason.
Where candidates lose it
Candidates compute each change separately and add them: leverage up two-thirds, rate up a fifth, so cover falls by something like 50 to 90% depending on how they combine it. Say the formula first, cover equals one over L times r, and the answer is a single division.
The second loss is treating 1.7x as comfortable because it is above one. The interviewer wants to hear that EBITDA is not cash available for interest.
What the interviewer asks next
- At 5x leverage, what rate would bring cover down to 1.0x?
- How would you compute cover after maintenance capex, and why is it lower?
- Which covenant would a lender set on this company, and at what level would you expect trouble?
031A software company has EBITDA of Rs 800 crore and debt of 7x EBITDA. If its EV/EBITDA multiple falls from 10x to 8x, what happens to its equity value, and what does 7x leverage tell you about the sensitivity?Moelis & CompanyNew York · 2026
Try it first
The multiple falls 20%, from 10x to 8x. Roughly how far does equity value fall?
Show the worked solution
Equity falls from Rs 2,400 crore to Rs 800 crore, a 66.7% drop on a 20% fall in EV. Debt is 7 x 800 = Rs 5,600 crore. At 10x, EV is Rs 8,000 crore; at 8x it is Rs 6,400 crore. Debt keeps its claim, so the equity slice absorbs the whole Rs 1,600 crore. At 7x leverage, equity moves 3.3 times as fast as EV, and a 7x multiple wipes it out.
Why does equity fall so much further than the business?
Think of a flat bought for Rs 1 crore with a Rs 70 lakh home loan. If the flat's price drops 20% to Rs 80 lakh, the bank still wants its Rs 70 lakh, so the owner's stake falls from Rs 30 lakh to Rs 10 lakh, a two-thirds loss. Debt is a fixed claim in rupees, so any change in enterprise value lands entirely on the equity that sits on top. Here debt is 7 x 800 = Rs 5,600 crore. At 10x, EV is Rs 8,000 crore and equity is Rs 2,400 crore, only 30% of the value.
With debt fixed at Rs 5,600 crore, a fall in the multiple from 10x to 8x takes EV from Rs 8,000 crore to Rs 6,400 crore and equity from Rs 2,400 crore to Rs 800 crore, a 66.7% loss on a 20% fall in EV, and at 7x the equity is gone. The relationshipE equity value: EV less debt EV enterprise value: EBITDA times the multiple EV/E the leverage multiplier, how many rupees of business each rupee of equity carries What it says in wordsThe percentage move in equity is the percentage move in EV multiplied by EV over equity.So what does 7x leverage tell you about sensitivity?
Leverage of 7x EBITDA means the debt alone is worth 7x EBITDA. Whenever the valuation multiple sits close to the leverage multiple, equity is a thin slice of the gap between them, and small changes in the multiple swing it hard. At 10x the gap is 3 turns; each turn of multiple is Rs 800 crore, a third of the equity. Software companies can carry this because their cash flows recur and their multiples are high, but the same 7x on a business valued at 8x leaves one turn of cushion. Say the limitation: the sum assumes debt is worth its face value, while in distress the debt itself would trade below par and soak up some of the loss.
Where candidates lose it
The common slip is answering 20%: the multiple fell 20%, so equity must too. That treats equity as if it were the whole business. Draw the stack, debt at the bottom in fixed rupees, and the answer is plain.
The second loss is giving the number without the read. The interviewer asked what 7x tells you, and the answer is a sentence about equity being a thin, highly geared slice whose value is the gap between two multiples.
What the interviewer asks next
- At what EV/EBITDA multiple is the equity worth exactly zero?
- If the company used Rs 800 crore of cash to repay debt first, how much would equity fall on the same de-rating?
- How would a lender look at the same 7x number differently from an equity investor?
Asked at Moelis & Company, Generalist, New York, 2026 (Wall Street Oasis):
A tech company has leverage rate of 7X. What does it tell you about the about the impact on sensitivity?
035A company trades at 2.0x book value. It has total assets of Rs 1,500 crore and a book debt-to-equity ratio of 0.5, with no other liabilities. What is its market capitalisation?EvercoreSan Francisco · 2026
Try it first
What is book equity here?
Show the worked solution
Market capitalisation is Rs 2,000 crore. With no other liabilities, assets equal debt plus equity. A D/E of 0.5 means debt is half of equity, so assets are 1.5 times equity and book equity is Rs 1,500 crore over 1.5, which is Rs 1,000 crore, with Rs 500 crore of debt. At 2.0x book, the market values that equity at Rs 2,000 crore.
How does a debt-to-equity ratio split the balance sheet?
Think of a Rs 15 lakh car bought with a loan that is half the size of your down payment. If the loan is half the down payment, the car cost one and a half down payments, so the down payment was Rs 10 lakh and the loan Rs 5 lakh. A D/E of 0.5 does not mean half the assets are debt; it means debt is half of equity, so assets are 1.5 times equity. Rs 1,500 crore over 1.5 gives book equity of Rs 1,000 crore and debt of Rs 500 crore.
A D/E of 0.5 splits Rs 1,500 crore of assets into Rs 1,000 crore of equity and Rs 500 crore of debt, and at 2.0x book the market values the equity at Rs 2,000 crore, not the Rs 1,500 crore you get by treating half the assets as equity. The relationshipP/B price to book: market value of equity over book equity D/E book debt over book equity 1 + D/E assets as a multiple of equity when there are no other liabilities What it says in wordsDivide assets by one plus the debt-to-equity ratio to get book equity, then apply the price-to-book multiple.What assumptions sit under the answer, and what could you add?
The question rules out other liabilities, such as payables and provisions, and that matters: a real balance sheet has plenty, and then assets are not just debt plus equity. Say the identity you are using, assets equal liabilities plus equity, before you lean on it. You can also go one step further than asked. With Rs 500 crore of debt and no cash given, enterprise value is about Rs 2,500 crore. And a P/B of 2.0 says the market thinks the assets earn more than their cost of capital; read it next to return on equity rather than on its own.
Where candidates lose it
The slip is reading D/E as debt over assets: half of Rs 1,500 crore is Rs 750 crore of equity, doubled to Rs 1,500 crore. Candidates do it because 0.5 sounds like half. Write D = 0.5E and the algebra decides for you.
The second loss is applying P/B to total assets. Price to book compares market value with book equity only, so the multiple must land on the Rs 1,000 crore, not on the Rs 1,500 crore.
What the interviewer asks next
- If the company also had Rs 300 crore of payables, what would market cap be?
- What return on equity would justify a P/B of 2.0 if the cost of equity is 12% and growth is zero?
- With Rs 200 crore of cash, what is enterprise value?
Asked at Evercore, Mergers and Acquisitions, San Francisco, 2026 (Wall Street Oasis):
Given P/B, total assets, and D/E ratio calculate Market Cap
036A business has a 10% operating margin. Next year revenue grows 20% and costs grow 15%. What is the new margin?Corporate FP&ABusiness finance
Try it first
Quick call: where does the margin land?
Show the worked solution
The new margin is 13.75%. Take revenue of 100, so cost is 90 and profit 10. Revenue grows to 120 and cost to 90 x 1.15 = 103.5, leaving profit of 16.5. The margin is 16.5 over 120, which is 13.75%. Profit itself grows 65%, because a 5 point gap between growth rates is large next to a 10% margin.
Why is the answer not simply 15%?
Think of a tea stall that takes in Rs 100 a day and spends Rs 90. If takings rise 20% and spending rises 15%, the extra takings are Rs 20 but the extra spending is Rs 13.50, because 15% is taken on 90, not on 100. Growth rates act on their own bases, so a margin moves by the gap in rupees, not by the gap in percentage points. Work in rupees on a base of 100 and the trap disappears: profit goes from 10 to 16.5 on revenue of 120.
On revenue of 100, profit of 10 gains 20 from revenue growth and loses 13.5 to cost growth, ending at 16.5 on revenue of 120, a margin of 13.75% rather than the 15% you get by adding the growth gap to the margin. The relationshipm0, m1 the old and new margins g_r, g_c revenue growth and cost growth 1 - m0 cost as a share of revenue before the change What it says in wordsThe new cost share is the old cost share scaled by cost growth over revenue growth, and the margin is what is left.Why does a thin margin make the move so large?
Profit is the small gap between two big numbers, so a modest difference in their growth rates is a big change to the gap. The thinner the starting margin, the more operating leverage a growth gap carries: here profit grows 65% on 20% revenue growth. Run the same 20% and 15% from a 30% margin and the new margin is 32.9%, a smaller relative move, because cost is a smaller share of revenue. Say the limit too: the formula assumes all cost grows at 15%. In practice fixed costs grow slowly and variable costs track volume, so you would split the cost line before trusting the answer.
Where candidates lose it
The fast wrong answer is 15%: 10% plus the 5 point gap between the growth rates. It treats both rates as if they applied to the same base, when cost growth applies to 90 and revenue growth to 100.
The second loss is stopping at the margin. The interviewer often wants the profit growth too, and 65% on 20% revenue growth is the sentence that shows you understand operating leverage.
What the interviewer asks next
- What cost growth would keep the margin at exactly 10%?
- If half the cost base is fixed and does not grow, what is the new margin?
- Revenue falls 10% and costs fall 5%. What happens to a 10% margin?
0391% of a company's invoices are fraudulent. A screening rule flags 90% of fraudulent invoices and 5% of clean ones. If an invoice is flagged, how likely is it to be fraud?Wolverine TradingChicago · 2017
Try it first
A flagged invoice: what is the chance it is really fraud?
Show the worked solution
About 15.4%. Picture 10,000 invoices. 100 are fraudulent and the screen flags 90 of them. 9,900 are clean and the screen flags 5% of them, 495. The flagged pile holds 585 invoices, of which 90 are fraud, so a flag means fraud only 90 times in 585. The rare base rate swamps the screen's accuracy.
Why is a 90% accurate screen right only 15% of the time?
Think of a smoke alarm that never misses a fire but also goes off whenever someone makes toast. In a house where fires are rare and toast is daily, almost every alarm is toast. When the thing you are hunting is rare, even a small false positive rate on the large innocent pile produces more false alarms than true hits. Here 5% of 9,900 clean invoices is 495 false flags, against only 90 true ones.
Of 10,000 invoices, the screen flags 90 of the 100 frauds and 495 of the 9,900 clean invoices, so the flagged pile of 585 is only 15.4% fraud even though the screen catches 90% of frauds. The relationshipP(F | flag) the chance an invoice is fraud given that it was flagged 0.01 the base rate of fraud 0.05 the false positive rate on clean invoices What it says in wordsTrue flags divided by all flags, where all flags include the false ones from the much larger clean pile.What would make the screen useful, and how would an auditor use it?
Cutting the false positive rate does far more than raising the catch rate. At a 0.5% false positive rate the flagged pile would be 90 frauds and about 49.5 clean invoices, and a flag would mean fraud 65% of the time. Raising the catch rate from 90% to 100% would only move the answer from 15.4% to about 16.8%. In practice a screen like this is a triage tool: it shrinks 10,000 invoices to 585 for a human to review, and that review is where the 495 false alarms are cleared. Say the limit too: the 1% base rate is itself an estimate, and the answer is only as good as it is.
Where candidates lose it
The trap answer is 90%, which swaps the chance of a flag given fraud for the chance of fraud given a flag. Interviewers ask this question to see whether you notice the swap.
Work in counts, not formulas. Saying "imagine 10,000 invoices" makes every number concrete, and the 495 false alarms jump out before you have written a single probability.
What the interviewer asks next
- If an invoice is flagged twice by two independent screens, what is the chance it is fraud?
- What false positive rate would make a flag mean fraud at least half the time?
- How would the answer change if fraud were 10% of invoices?
Asked at Wolverine Trading, Prop Trading, Chicago, 2017 (Wall Street Oasis):
Phone interviews were pretty standard brainteasers and fit questions. There was a Bayes question
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
Try it first
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?
