Derivatives Foundation interview preparation

Questions

100

Traced to a firm

29

Firms

19

Updated

September 2026

Asked at

All firmsMSMorgan Stanley4Nomura4Akuna Capital2Amundi2HSBC2PIMCO2Bank of America1Barclays1Citadel1DRW1Goldman Sachs1Jane Street1Millennium Management1Mizuho1Old Mission Capital1RCRBC Capital Markets1Scotiabank1UBS1Wells Fargo Securities1

Topic

All topicsForwards and futures10Options basics8Option pricing7The Greeks10Volatility7Option strategies9Swaps and rates7Credit derivatives4Market structure and clearing6Indian derivatives8Trading and markets9Brainteasers6Fit9

Level

AnyCoreIntermediateHard

Type

AnyTechnicalCaseMarket viewBrainteaserFit

1. 090How many taxis are there in Hong Kong Central?BrainteasersIntermediatetechnicalHSBCSales and Trading · Hong Kong · 2026

   Say this

   I would build it from demand rather than guess at a fleet. Central has roughly 250,000 to 300,000 daytime workers and visitors, say 10 percent take a taxi on a given day, so about 25,000 to 30,000 trips. A taxi does maybe 25 trips a day, so around 1,000 to 1,200 taxis serving Central at any time. As a sanity check, Hong Kong licenses about 18,000 taxis in total, so Central holding 5 to 7 percent of them is plausible.

   Then walk it

   1. State the approach before the arithmetic: demand side, because I can estimate people and trips more reliably than I can estimate a fleet directly.
   2. Population of Central during the working day: it is a dense financial district, so a few hundred thousand is the right order. I would say 250,000 and flag that as my biggest uncertainty.
   3. Trips per person per day: most people walk or take the MTR in Central because it is compact and well-served, so I would use 10 percent rather than something higher. That gives 25,000 trips.
   4. Trips per taxi per day: a 10-hour shift with an average trip and repositioning taking 20 to 25 minutes gives roughly 25 trips. So 25,000 over 25 is about 1,000 taxis.
   5. Then the cross-check from the supply side, which is what makes the answer credible: Hong Kong's total licensed fleet is around 18,000, a number that is publicly known and stable because licences are capped. My 1,000 to 1,200 for Central is a believable share of it.
   6. And I would name the sensitivity: the answer is most sensitive to the trips-per-person assumption. Double it to 20 percent and I get 2,000 taxis. So my honest answer is a range of roughly 1,000 to 2,000 with a central case around 1,200, and I would want the actual taxi stand data to tighten it.

   Where candidates lose it

   Guessing a number and then rationalising it. And in Hong Kong specifically, ignoring that Central is compact and MTR-dense — a candidate who uses a New York taxi propensity will be out by a factor of three. Cross-check from the licensed fleet, and name which assumption drives the answer.

   Expect next

   • Which assumption is your answer most sensitive to?
   • Now do it as a fleet-size estimate and see if the two agree.
   • How many beds are there in a New York hotel?

   Reported by candidates at HSBC (Sales and Trading, Hong Kong, 2026). Source: Wall Street Oasis.

2. 091How many beds are there in a New York hotel?BrainteasersCoretechnicalHSBCSales and Trading · Hong Kong · 2026

   Say this

   Around 250 to 350 beds for a typical mid-size Manhattan hotel. Build it from the building: about 20 floors, roughly 12 rooms per floor, so around 240 rooms, and about 1.3 beds per room once you account for doubles and suites. That gives roughly 300 beds.

   Then walk it

   1. Clarify the question first — one hotel, not the city, and a typical hotel rather than a specific one. Asking that takes five seconds and prevents answering the wrong question.
   2. Build from the physical structure: a Manhattan hotel on a standard lot, 20 floors, a floor plate that fits about 12 rooms around a central corridor. That is roughly 240 rooms.
   3. Beds per room: most rooms have either one king or two queens. Call it 60 percent single-bed and 40 percent double, so about 1.4 beds a room, less a few floors for lobby, function space and back of house. Round to 300 beds.
   4. Sanity check against known anchors: New York has roughly 120,000 to 140,000 hotel rooms across about 700 hotels, which is an average of about 180 to 200 rooms per property. So my 240 is on the larger side of average, which is fine if I say I am describing a mid-to-large hotel.
   5. That cross-check is the part that earns credit, because it shows I hold one or two real anchor numbers and use them to test a bottom-up estimate rather than relying on either alone.
   6. I would close with the range and the driver: 250 to 350 for a typical property, and the answer scales almost entirely with floors times rooms per floor, so if you tell me it is a 40-storey tower I would double it. Naming what the answer is a function of matters more than the point estimate.

   Where candidates lose it

   Answering a different question — beds in all New York hotels — or giving a number with no structure. Estimation questions are graded on the decomposition and the cross-check, not on accuracy. Build it, then test it against one anchor you actually know.

   Expect next

   • Now estimate the total number of hotel rooms in New York.
   • What is the occupancy rate, and what would that imply for revenue?
   • Which of your assumptions would you check first?

   Reported by candidates at HSBC (Sales and Trading, Hong Kong, 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.