Derivatives Foundation interview preparation

The full derivatives syllabus from no-arbitrage pricing through the Greeks, the volatility surface, swaps, CDS and clearing, plus the Indian index-options market. Every question is either traced to a named firm from a public candidate report, or tagged at desk level when we could not trace it - we do not invent attributions.

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100 questions, mapped to the firms that asked them

Questions: 100
Traced to a firm: 29
Firms: 19
Updated: September 2026

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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.

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.

100 questions, mapped to the firms that asked them

Say this

Then walk it

Where candidates lose it

Expect next