Quant interview preparation

Prop market making and quantitative research, weighted the way the interviews actually are: probability and expected value, statistics and machine learning, market making logic, programming and options. 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, and every probability answer shows the reasoning path rather than just the number.

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100 questions, mapped to the firms that asked them

Questions
100
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53
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Updated
September 2026
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All firmsOld Mission Capital12Tower Research Capital10Jump Trading7Akuna Capital5Citadel4D.E. Shaw3Jane Street3AQR Capital Management2DRW2Millennium Management2Schonfeld2Squarepoint Capital2Susquehanna International Group2Belvedere Trading1Optiver1
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All topicsProbability10Coins, cards and games6Expected value8Statistics11Market making15Estimation and mental maths4Stochastic processes4Regression5Machine learning6Time series6Programming10Options and derivatives8Fit and motivation7
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  1. 020How many zeros are at the end of a thousand factorial?Estimation and mental mathsCorephone / first roundJump TradingTrading · Chicago · 2013

    Say this

    249. A trailing zero needs a factor of ten, which needs a two and a five, and fives are scarcer than twos, so just count the fives: 200 plus 40 plus 8 plus 1 equals 249.

    Then walk it

    1. Trailing zeros equal the number of times 10 divides the number, which is the minimum of the exponent of 2 and the exponent of 5 in the prime factorisation. In a factorial, 5 always binds.
    2. Legendre's formula: sum of floor(1000 divided by 5 to the k). That is floor(1000/5) equals 200, floor(1000/25) equals 40, floor(1000/125) equals 8, floor(1000/625) equals 1, and floor(1000/3125) equals 0.
    3. 200 plus 40 plus 8 plus 1 gives 249.
    4. Why the higher powers: 25 contributes two fives, not one, so it must be counted again. Missing that is the single most common error and it costs you 49.
    5. Quick sanity check on the order of magnitude: roughly 1000/4 is 250, because each multiple of five contributes one and a bit. 249 sits right where it should.

    Where candidates lose it

    Answering 200 by counting only the multiples of five. Multiples of 25, 125 and 625 carry extra factors of five and each must be counted again. Say out loud why five binds rather than two, because that is the part of the reasoning being graded.

    Expect next

    • How many zeros in 100 factorial?
    • How many digits does 1000 factorial have?
    • What is the last non-zero digit of 100 factorial?

    Reported by candidates at Jump Trading (Trading, Chicago, 2013). 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.