Investment Banking puzzles, solved step by step

Net income falls Rs 7.5, cash rises Rs 2.5, inventory falls Rs 10 and retained earnings fall Rs 7.5. The write-down is an expense, so pre-tax income falls 10 and, after the Rs 2.5 tax saving, net income falls 7.5. No cash left the business, so the cash flow statement adds the 10 back and cash ends Rs 2.5 higher. Assets fall 7.5 and equity falls 7.5, so it balances.

Why does a loss leave the company with more cash?

A shopkeeper finds a carton of biscuits past their date. They cost Rs 10 and are now worth nothing. No money changes hands today; the cash went out when the biscuits were bought. What changes is that the loss lowers this year's taxable profit. A write-down is a non-cash loss, so its only cash effect is the tax it saves, and cash rises by 25% of Rs 10. Inventory is carried at the lower of cost and net realisable valueWhat the stock can be sold for, less the costs of selling it., which is why the carrying amount is cut when goods lose value.

How does each statement move?

Income statement: the write-down usually sits inside cost of goods sold, so pre-tax income falls 10, tax falls 2.5 at 25%, and net income falls 7.5. Cash flow statement: start from net income of minus 7.5, add back the 10 because no cash left, and operating cash flow is plus 2.5. Balance sheet: inventory is down 10 and cash is up 2.5, so total assets are down 7.5, and retained earnings are down 7.5. The check is minus 10 plus 2.5 on the asset side equalling minus 7.5 in equity.

What assumption should you say out loud?

That the write-down is deductible for tax now, as the question states. Whether a tax system allows the deduction when the stock is written down or only when it is sold depends on its rules, which you would confirm. If the deduction comes later, cash does not move this year and the company records a deferred tax asset of Rs 2.5 instead, with the balance sheet still balancing. Offering that variant in one sentence shows you understand why the cash moved in the first place.

Light rope A at both ends and rope B at one end at the same moment. When A burns out, 30 minutes have passed: light B's other end, and B burns out 15 minutes later, at 45 minutes. Lighting a rope at both ends halves whatever burning time it has left, however unevenly it burns, so B's remaining 30 minutes take 15.

Why can you not just cut a rope into pieces?

Because uneven burning means length tells you nothing about time. Think of a candle with a thick base and a thin top: half its height might burn in ten minutes or in forty. The only thing you know for certain about each rope is its total burning time, 60 minutes, so every step must work with time, never with length. Cutting, folding or marking a rope uses length, which is why every answer built on them fails.

Why does lighting both ends halve the time?

Picture the rope as a row of short segments, each with its own burning time, adding up to 60 minutes. Two flames eat into the row from both ends at the same moment and meet somewhere. When they meet, each has burned for the same length of time, and between them they have consumed all 60 minutes of segments. Two flames sharing 60 minutes of burning finish in 30, wherever along the rope they happen to meet. The same holds for a rope with any amount of burning time left: lit at both ends, it lasts half that.

How does that build 45 minutes?

Light A at both ends and B at one end at time zero. A is gone at 30 minutes, which is your signal. B has burned for 30 minutes from one end, so exactly 30 minutes of burning time remain in it, wherever the flame has reached. Light B's other end at that moment and those 30 minutes burn in 15. B goes out at 30 plus 15, which is 45 minutes, and no step relied on length. Say the answer as three events with clock times, 0, 30 and 45, so the interviewer can follow each one.

About 8 years: 72 divided by 9 is 8.0, and the exact answer is 8.04 years. The exact doubling time is the log of 2 divided by the log of 1.09. The rule is a shortcut built for moderate rates: it is almost exact around 8%, slightly long at low rates and increasingly short at high ones. At 40% it says 1.8 years against an exact 2.06.

Why does 72 work at all?

Think of a sapling that grows 9% taller each year; the question is how many of those steps multiply up to 2. The exact answer uses logarithms: years equal ln 2 divided by ln(1 + r). For small r, ln(1 + r) is close to r, and ln 2 is 0.693, so the exact rule is close to 69.3 divided by the rate in per cent. 72 replaces 69.3 because it divides cleanly by 2, 3, 4, 6, 8, 9 and 12, and because ln(1 + r) sits below r at the rates people actually meet, which pushes the true constant up. At 9%, ln 1.09 is 0.0862, and 0.693 / 0.0862 is 8.04.

Where does the rule break down?

At high rates. ln(1 + r) falls further below r as r grows, so the true doubling time is longer than 72 divided by r: at 20% the rule says 3.6 years against 3.80, and at 40% it says 1.8 against 2.06, an error of 12.6%. At very low rates it errs the other way: 36 years against 35.0 at 2%. The rule is within about 1% of the exact answer only between roughly 6% and 10%, and should be adjusted outside that band.

A common adjustment for high rates adds one to the 72 for every three points of rate above 8%. At 20% that gives 76 divided by 20, 3.80 years, and at 40% about 82.7 divided by 40, 2.07 years, both within a hundredth or two of the exact figures. For deal work, where target returns of 20% to 30% are common, that adjustment is worth knowing.

Roughly Rs 2.3 lakh crore a year, on stated assumptions. Assume about 90 lakh weddings a year, from a population of about 140 crore. Split them into budget, mid-range and premium tiers, each with its own plate count and cost per plate. Budget weddings contribute about Rs 47,000 crore, mid-range Rs 81,000 crore and premium about Rs 1 lakh crore: 5% of weddings, 44% of the spend.

How many weddings happen a year?

Start from people, not from a remembered statistic. Assume a population of about 140 crore, a figure to confirm, and an average lifespan near 70 years, so roughly one seventieth of people, 2 crore, reach marrying age each year. Assume 90% marry: 1.8 crore people, or 90 lakh weddings. A count built from cohorts can be checked line by line, which is what makes it defensible in the room. One caveat is worth saying: a young population has larger cohorts than one seventieth, so this may undercount a little.

Why split by tier rather than use one average wedding?

Think of a school canteen and a five-star hotel both serving lunch. Averaging their prices and their customer counts separately, then multiplying, gives a number neither of them earns. Big weddings have both more guests and a higher cost per plate, so averaging guests and price separately understates the market. On the tiers below, the average-wedding shortcut, 435 plates at Rs 400, gives Rs 1.57 lakh crore, about 32% less than the tiered Rs 2.29 lakh crore. Plates here count every guest meal across all the functions of a wedding, and catering means food only, not venue or decoration.

Which assumption moves the answer most?

The premium tier. It is 5% of weddings and 44% of the value, so a change in its plate count or price moves the total more than any change in the budget tier. When one segment dominates the value, spend your sanity checks there: is 1,500 plates across several functions at Rs 1,500 a plate plausible for the top twentieth of weddings? Halve the premium tier's value and the total falls to about Rs 1.8 lakh crore, which is the honest low end of the range to quote.

115.6. Notice that 34% of 170 is the same as 17% of 340: halving one number and doubling the other leaves a product unchanged. So the sum is 17% of 340 twice, which is 34% of 340. That is 30% of 340, which is 102, plus 4% of 340, which is 13.6, giving 115.6.

What is the trick hiding in the numbers?

Two plots of land, one 34 metres by 17 and one 17 metres by 34, have the same area; turning a rectangle on its side does not change it. Percentages behave the same way, because x% of y is x times y divided by 100. The percentage and the base can trade places, so 34% of 170 equals 17% of 340: each is 17 x 340 / 100, which is 57.8. Once you see that, the question is one product, not two.

How do you do 34% of 340 in your head?

Split it into easy pieces: 30% of 340 is 102 and 4% of 340 is 13.6, so the total is 115.6. Or notice that 34% of 340 is 34 x 3.4, and 34 x 34 is 1,156, so the answer is 115.6. Spotting a structure first and calculating second is the habit the interviewer is checking, and it usually turns two awkward products into one easy one.

How do you check it before you say it?

Estimate first: 17% is a little more than a sixth, and a sixth of 340 is about 57, so each term is near 57 and the sum near 115. Then check each term directly: 10% of 340 is 34 and 7% is 23.8, so 17% is 57.8; 30% of 170 is 51 and 4% is 6.8, so 34% of 170 is 57.8. The two terms match, which confirms the swap.

Expected wealth is Rs 9.31 lakh, but the most likely outcome is Rs 1 lakh, exactly where you started. Each round multiplies the stake by 1.25 on average, and 1.25 to the tenth is 9.31. Yet the wealth you actually hold is 2 to the power of heads minus tails, and the likeliest split is five and five, which multiplies to one. The median player goes nowhere; the mean is carried by a handful of lucky runs.

Why is the average so far from the typical result?

Ten friends each put Rs 1 lakh into this game. Most finish near where they began, a few lose most of their money, and one, with a long run of heads, finishes with hundreds of lakh. Add it all up and divide by ten and the average looks wonderful; ask the friend in the middle how it went and the answer is that nothing happened. Gains and losses compound, and a doubling followed by a halving lands exactly back where you started, so the mean grows 25% a round while the median stays flat. The arithmetic average of 2 and 0.5 is 1.25; their geometric average, the square root of 2 times 0.5, is exactly 1, and compounding follows the geometric one.

How do you get both numbers in two lines?

For the mean, use the fact that the expectation of a product of independent rounds is the product of the expectations: 1.25 to the tenth, 9.31. For the typical outcome, count heads. After ten flips the wealth is Rs 1 lakh times 2 to the power of heads minus tails, which is 2 to the power of 2H minus 10. Five heads is the single likeliest count, 24.6% of games, and it gives a multiplier of exactly one; it is also the median, because the outcomes sit symmetrically on either side of it. 37.7% of players finish below Rs 1 lakh and the same share above, and you can say all of that without touching the mean.

Where does the Rs 9.31 lakh come from, then?

From the tail. A run of ten heads happens once in 1,024 games and turns Rs 1 lakh into Rs 1,024 lakh, which on its own adds a full Rs 1 lakh to the mean. The three best outcomes, eight or more heads, occur in 5.5% of games and contribute Rs 6.31 lakh of the Rs 9.31 lakh average, about 68% of it. Nothing is wrong with the expected value; it is the wrong statistic for a question about what will probably happen to you. The right one is the geometric meanThe growth rate that compounding actually delivers: the nth root of the product of n multipliers. It is never above the arithmetic mean. return, which here is zero.

The lesson a desk draws is about sizing. Bet only half your stake each round and the multipliers become 1.5 and 0.75, whose geometric mean is 1.0607: the typical player now grows about 6.1% a round and finishes ten rounds near Rs 1.80 lakh, even though the expected value per round has fallen from 1.25 to 1.125. Half is the fraction that maximises the typical growth rate in this game. The same arithmetic sits under volatility drag in fund returns: a strategy that gains 50% and then loses a third has a flattering average and nothing to show for it.

Enterprise value is Rs 1,320 crore. Start with equity value of Rs 1,000 crore. Add the claims that rank alongside or ahead of the ordinary shareholders on the consolidated business: debt of Rs 400 crore, preference shares of Rs 100 crore and minority interest of Rs 50 crore. Subtract what the company owns that is not part of that operating business: cash of Rs 150 crore and the Rs 80 crore associate stake. 1,000 plus 550 less 230 is 1,320.

Why are some items added and others subtracted?

Picture buying a shop. You pay the owner for her shares, but you also take on the bank loan, you owe the silent partner his share of the profits, and you inherit the cash in the till and the shop's small stake in the bakery next door. The price of the shop itself is what you paid, plus the loan and the partner's claim, minus the cash and the bakery stake, which you could sell on day one without touching the shop. Enterprise value is the value of the consolidated operating business, so you add every claim on that business and subtract every asset whose earnings sit outside it.

What is the test for each line?

Ask where the item's earnings appear. Minority interestThe share of a consolidated subsidiary owned by outside shareholders. Its profit is inside consolidated EBITDA but belongs to someone else. is added because consolidation puts 100% of the subsidiary's EBITDA into the group figure even though outsiders own part of it; leave it out and EV is too small for the EBITDA it is set against. Preference shares are added because their dividend is a claim ahead of the ordinary equity. The associateA company in which the group holds a significant but not controlling stake, usually 20% to 50%, shown as one line of share of profit below operating profit. is subtracted for the mirror reason: its profits arrive as a single line below EBITDA, so its value must come out of the numerator to keep the multiple consistent. The rule is consistency between numerator and denominator: EV must describe exactly the business whose EBITDA you divide it by.

What would you say the question leaves out?

Three things an interviewer may push on. Net debt here is Rs 250 crore, but a company needs some cash to run, so only the excess is truly surplus; most desks ignore that in an interview and net all of it, which is the assumption to state. Debt-like items such as unfunded pension deficits, lease liabilities and earn-outs also belong on the add side, and an interviewer who adds a convertible bond is checking whether you treat it as debt or as equity at the current share price. Give the Rs 1,320 crore, then name one debt-like item you would ask about, because the bridge in a live deal is longer than the one in the question. The multiple this feeds, EV/EBITDA, is only as clean as the bridge beneath it.

The value falls, by about 4.8% here, because the cut to cash flow outweighs the cheaper debt. One: unlevered free cash flow falls, as NOPAT drops from Rs 150 crore to Rs 140 crore. Two: the after-tax cost of debt falls from 6.0% to 5.6%, taking the WACC from 10.20% to 10.08%. Three: the terminal value, which carries both effects, falls from about Rs 2,516 crore to Rs 2,395 crore at 4% growth.

Why does a tax rate touch both the top and the bottom of the fraction?

A landlord pays more tax on her rent, so the rent she keeps falls; but the interest on her mortgage is deductible, so the loan costs her a little less after tax. Two opposite effects from one change. A DCF is the same fraction: cash flow on top, discount rate below. A higher tax rate shrinks the cash flows directly and shrinks the WACC indirectly through the interest tax shield, and the first effect is almost always larger because it hits every rupee of operating profit while the second touches only the debt slice. Interviewers ask for three ways so that you show both sides and then say which wins.

How big is each effect on these numbers?

Cash flow. NOPAT is EBIT times one minus the tax rate: Rs 200 crore x 0.75 = Rs 150 crore before and Rs 200 crore x 0.70 = Rs 140 crore after, a fall of Rs 10 crore, or 6.7%, in every forecast year, treating depreciation, capex and working capital as cancelling out. Discount rate. The after-tax cost of debt is 8% x (1 - t): 6.0% before and 5.6% after. Weighted at 30% debt and 70% equity at 12%, the WACC moves from 10.20% to 10.08%, down 12 basis points. Terminal value. At 4% growth, a Gordon growthA terminal value that treats the final cash flow as growing at a constant rate forever: the next cash flow divided by the discount rate less the growth rate. terminal value is Rs 2,516 crore before and Rs 2,395 crore after. Separating the two, the cash flow cut alone takes Rs 168 crore off the terminal value and the lower WACC alone adds Rs 46 crore back, so the net is Rs 121 crore, 4.8% lower.

Is there a subtler channel the interviewer might be after?

Yes: the cost of equity. When you relever a beta, the formula carries a (1 - t) term, so a higher tax rate lowers the levered beta a little and the cost of equity with it. With debt to equity of 3 to 7 and a levered beta of 1.0 at 25%, the unlevered beta is 0.757, and relevering at 30% gives 0.984; with an assumed 6% risk-free rate and 6% equity risk premium, the cost of equity slips from 12% to 11.90% and the WACC to 10.01%. Even with that help the value is still about 3.7% lower, so the ranking of the effects does not change. Say the limitation too: the WACC relief assumes the company actually pays tax and keeps its interest deductible, and interest deductions are capped in many jurisdictions, a rule to confirm for the country in question.

The lottery ticket has a beta of zero, and the half-and-half portfolio has a beta of 0.5. Beta is the covariance of an asset's return with the market's return divided by the market's variance. A lottery draw does not move with the index at all, so its covariance is zero, however wild its payoff. Betas combine in proportion to weights, so half an index fund at beta 1 and half tickets at beta 0 give 0.5 x 1 + 0.5 x 0 = 0.5.

Why is a wildly risky asset given a beta of zero?

Think of two shops on one street. One sells umbrellas, whose takings rise and fall with the weather; the other sells birthday cards, whose takings have nothing to do with it. The card shop's sales swing plenty, but not with the rain. Beta measures only the part of an asset's movement that follows the market, so an asset whose payoff is decided by a draw of numbered balls has a beta of zero no matter how large its swings. On a Rs 10 ticket with an assumed one in a crore chance of a Rs 5 crore prize, the standard deviation of the return is about 1,600 times the stake and the beta is still zero. Volatility is total riskThe full spread of an asset's returns, usually measured by standard deviation, including both the part linked to the market and the part unique to the asset.; beta is only its market-linked part.

How does the portfolio beta follow?

Covariance is linear in the weights, so the beta of a portfolio is the weighted average of the betas inside it. An index fund tracking the market has a beta of one by construction. Half at beta 1 and half at beta 0 gives 0.5, the same beta as a portfolio that is half the index and half cash. That comparison is the point: in the capital asset pricing model the lottery half and a cash half demand the same return, the risk-free rate, because neither adds market risk; the lottery's enormous extra risk is diversifiable in theory and simply unrewarded.

What does the security market line say about the blend?

Plot required return against beta. With an assumed 6% risk-free rate and 6% equity premium, the line runs from 6% at beta 0 to 12% at beta 1, and the blend at beta 0.5 would be required to earn 9%. Its expected return is nothing like that: if a ticket pays out an assumed half of its price in prizes, its expected return is -50%, and the blend's is 0.5 x 12% plus 0.5 x -50%, which is -19%. Beta tells you where an asset sits along the line, and the lottery ticket sits about 56 points below it: a zero-beta asset with an appalling expected return. That is the limitation to state: beta says nothing about expected return outside the model's assumptions, and nothing about risk the market does not share.

Why a banker asks it: the same logic decides what goes into a cost of equity. A project whose cash flows do not move with the economy, a regulated pipeline or a contracted toll road, carries a low beta and a low cost of equity even if its engineering risk is large, because that risk is specific and diversifiable. Candidates who confuse volatility with beta tend to over-discount exactly those assets, and to under-discount a cyclical business that happens to look calm.

About Rs 27.3 lakh, the value of selling it. Keeping the elephant forever costs Rs 20 lakh a year, minus Rs 2 crore in today's money at 10%. Selling means one more year of upkeep and Rs 50 lakh at the end, a net Rs 30 lakh worth Rs 27.3 lakh today. Donating is worth zero. A gift is worth its best use, and the free exit means it can never be worth less than zero.

Why does the elephant not have one value?

Think of being handed an old car that needs Rs 30,000 of repairs before anyone will buy it. The car is not worth its sticker price; it is worth what you can do with it, net of what doing that costs. An asset with a carrying cost has no value of its own: each option for it has a value, and the asset is worth the best of them. So the first move is to list the options out loud, keep it, sell it or give it away, and then price each one at the same 10% rate.

How do you price each option?

Keeping is a perpetuityA payment that repeats every year forever. Its value today is the yearly amount divided by the discount rate. of costs: Rs 20 lakh a year divided by 10% is minus Rs 200 lakh, or minus Rs 2 crore. Selling means paying one more year of upkeep while the paperwork clears, then collecting Rs 50 lakh. Net of upkeep, the sale delivers Rs 30 lakh at the end of year one, and Rs 30 lakh a year away is worth Rs 27.3 lakh today. Donating costs nothing and brings nothing. The working assumes upkeep is paid at the year end; if it is paid upfront, the sale is worth Rs 25.5 lakh instead, and the choice does not change.

When would the gift be worth nothing?

Change one number. If the best sale price were Rs 15 lakh, the sale would net minus Rs 5 lakh at the year end, minus Rs 4.5 lakh today, and donating would win at zero. The free exit puts a floor under the gift: it can be worth nothing, but never less than nothing, as long as someone will take it away for free. Remove the sanctuary and the floor goes too. That is why bankers ask about exit options before valuing a loss-making plant, a lease that cannot be broken or a subsidiary with heavy fixed costs.