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Citadel Securities · Quant researcher · Quant Research (new grad & experienced)

QR: Probability, Statistics & Brainteasers

Rapid-fire spoken probability and statistics with escalating follow-ups and variations

What they actually ask

The question shapes this round uses. Larpy does not read these out. It builds each one from your own resume, because the generic version is the one you have already rehearsed.

  • “Expected number of coin flips to first see two heads in a row versus heads-then-tails, and why they differ.”
  • “A gambler bets $1 repeatedly with fixed win probability; what is the chance of reaching $N before going broke? (gambler's ruin)”
  • “N people throw their hats in a pile and each picks one at random; expected number who get their own hat back?”
  • “Break a stick at two uniformly random points; what is the probability the three pieces form a triangle?”
  • “Estimate a Fermi-style quantity out loud (e.g. daily volume of a market) and walk through your assumptions.”

What this round is judged on

  • Probability fluency · expected value, conditioning, Bayesian updates
  • Rigor · set up and solve cleanly, then generalize
  • Mental math · quick, accurate arithmetic under pressure
  • Composure · reason out loud and recover from mistakes
  • Estimation · structured Fermi reasoning

Where this round sits

Citadel Securities’s published process. Lime marks the stage this round runs.

  1. 01
    Application / resume screen
  2. 02
    Online assessment (OA)
  3. 03
    Technical phone screen
  4. 04
    Onsite / Superdaythis round
  5. 05
    Hiring decision / committee
What happens in each stage›
Application / resume screen
Recruiter and/or hiring-team screen of resume and background against the target level. SWE and Quant Research (QR) are distinct tracks with overlapping but different loops.
Online assessment (OA)
SWE: HackerRank (occasionally CodeSignal), typically 2-3 hard algorithmic problems, ~60-90 min, strong DS&A bar. QR: heavier probability/statistics/math plus some Python. Format and vendor vary by cycle and campus.
Technical phone screen
One live coding interview (CodePair-style shared editor), ~45-60 min, DS&A focused for SWE. QR phone screens skew to probability, statistics, brainteasers, mental math and light coding.
Onsite / Superday
Multiple back-to-back rounds. SWE commonly: the signature 'evolving problem' coding round, one or more DS&A rounds, a systems / low-level fundamentals conversation (C++ / memory / concurrency), and a behavioral / motivation round. QR: probability & statistics deep-dive, a Python/data coding round, a stats/ML modeling conversation, and a fit round.
Hiring decision / committee
Debrief and hiring decision. Bar is high; strong DS&A and clean, adaptable design are consistently emphasized.

Sources

Built from what Citadel Securities publishes about its own process and from real interview data. No leaked question lists. The questions you get are generated against your own resume, so they are not from anyone else's interview.

Sources last checked . Hiring loops change, so this date is the honest limit on everything above.

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