Investment Banking interview preparation

Questions

100

Traced to a firm

100

Firms

46

Updated

September 2026

Asked at

All firmsTSTruist Securities10Rothschild & Co8Centerview Partners7CSCredit Suisse7HWHarris Williams6Houlihan Lokey6Lazard6Mizuho6Barclays5Citi5Deutsche Bank5Evercore5Moelis & Company5MSMorgan Stanley5Piper Sandler5RCRBC Capital Markets5Goldman Sachs4Nomura4TD Securities4Bank of America3GSGuggenheim Securities3J.P. Morgan3Jefferies3Moody's3Perella Weinberg Partners3WPWarburg Pincus3WBWilliam Blair3HSBC2Lincoln International2Scotiabank2TPTPG2UBS2Wells Fargo Securities2Advent International1Apollo Global Management1Bain Capital1Balyasny Asset Management1BLBlackRock1BPBNP Paribas1General Atlantic1Invesco1Morningstar1PIMCO1STSociété Générale1SSState Street1WMWellington Management1

Topic

All topicsAccounting14Valuation21M&A10Markets and deals10Capital markets3LBO8Leveraged finance3Restructuring2Credit3Debt capital markets2Capital structure2Case and estimation11Brainteasers6Fit5

Level

AnyCoreIntermediateHard

Type

AnyTechnicalCaseBrainteaserFitMarket view

1. 092I paint the surface of a 10x10x10 cube green. How many of the small cubes have green on them, and how many do not?BrainteasersIntermediatetechnicalTD SecuritiesGeneralist · New York · 2024

   Say this

   488 have green on them and 512 do not. Solve the easy half first: the unpainted cubes form an inner 8x8x8 block, which is 512. Subtract that from 1,000 to get 488 painted.

   Then walk it

   1. Total small cubes: 10 cubed is 1,000.
   2. Any cube not touching the surface is one layer in from every face. That leaves an 8 by 8 by 8 core, because you remove one layer from each of the two opposite sides in all three dimensions.
   3. 8 cubed is 512 unpainted.
   4. So painted is 1,000 minus 512, which is 488. Computing the painted faces directly is possible but far more error-prone.
   5. If they push further: 8 corner cubes have three painted faces, 96 edge cubes have two, and 384 face cubes have one. That sums to 488, which confirms the answer.

   Where candidates lose it

   Trying to count the painted cubes face by face and double-counting the edges and corners. Always solve for the interior and subtract. Saying 'I will do the easy side first' out loud is itself the signal they want.

   Expect next

   • How many have exactly two painted faces?
   • Generalise it for an n-cube.
   • Now do it for a 10x10x10 where I only paint the top and bottom.

   Reported by candidates at TD Securities (Generalist, New York, 2024). Source: Wall Street Oasis.

2. 094How many aeroplanes are in the air at once?BrainteasersIntermediatetechnicalSTSociété GénéraleMergers and Acquisitions · New York · 2025HSBCSales and Trading · Hong Kong · 2026

   Say this

   Around ten to fifteen thousand. Build it from the fleet: roughly 25,000 commercial aircraft worldwide, each flying maybe 10 hours a day, so about 40 percent are airborne at any moment, which gives 10,000.

   Then walk it

   1. Start from a number you can defend: the global commercial fleet is on the order of 25,000 aircraft. If you do not know it, build it from airlines: a few hundred carriers averaging perhaps 80 aircraft.
   2. Utilisation: a commercial jet flies roughly 8 to 12 hours a day. Call it 10, which is about 40 percent of a 24-hour day.
   3. 25,000 times 0.4 gives 10,000 airborne on average.
   4. Then adjust for the peak-trough pattern. Air traffic is concentrated in daylight hours across the Northern Hemisphere, so the daytime peak might be 50 percent above average and the small hours well below. Peak perhaps 15,000.
   5. Then say what you excluded and why: private aviation, cargo and military would add to it, probably a few thousand more, and I have not counted them.
   6. Close with the sanity check: published flight-tracking figures sit in the same range, low to mid five figures, so the estimate holds.

   Where candidates lose it

   Guessing a number with no derivation, or getting lost in decimals. Market sizing is judged entirely on structure. State each assumption, keep the arithmetic round, and say which populations you left out.

   Expect next

   • How many taxis are in Hong Kong Central?
   • How many hotel beds are there in New York City?
   • How many books were sold in the US last year?

   Reported by candidates at Société Générale (Mergers and Acquisitions, New York, 2025); HSBC (Sales and Trading, Hong Kong, 2026). Source: Wall Street Oasis.

3. 095What is 301 times 447?BrainteasersIntermediatetechnicalGeneral AtlanticGeneralist · New York · 2026

   Say this

   134,547. Break 301 into 300 plus 1. Three hundred times 447 is 134,100, plus one more 447 gives 134,547.

   Then walk it

   1. Decompose to the nearest round number. 301 is 300 plus 1, and 300 is easy because it is 3 times 100.
   2. 447 times 3 is 1,341. Times 100 is 134,100.
   3. Add the remaining 447: 134,547.
   4. Announce the decomposition before you compute, so the interviewer can follow and so a slip in arithmetic does not look like a failure of method.
   5. The same trick handles most of these: round one number, multiply, then correct. For 19 times 63, do 20 times 63 minus 63.

   Where candidates lose it

   Attempting long multiplication in your head and losing a digit. These are speed-and-method tests. Decompose out loud, keep one running total, and offer the sanity check that the answer should be a bit over 134,000.

   Expect next

   • What is 19 times 63?
   • What is 1/7 as a decimal?
   • What is the square root of 6,241?

   Reported by candidates at General Atlantic (Generalist, New York, 2026). Source: Wall Street Oasis.

Firm tags come from public, anonymous candidate reports on Wall Street Oasis: strong signal, not sworn testimony. Firms are named as the places a question was reported, not as partners of Fin Maverick. Answers are written for this page to show how to think out loud; they are not scripts to recite.