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Jane Street interview questions

104 questions researched across 4 Jane Street seats in Trading, Research, Technology. Below are 12 of them.

Seats we researched

  • Quantitative Trader InternTrading · intern · 30 min
  • Quantitative Researcher InternResearch · intern · 30 min
  • Software Engineer InternTechnology · intern · 45 min
  • Quantitative TraderTrading · graduate · 30 min

12 Jane Street interview questions

  1. New game. I roll a die and pay you what it shows in dollars, but you may reroll up to two times, and you keep the last roll you take. How much would you pay to play?

  2. How confident are you in that answer, as a number between zero and one?

  3. If you toss a fair coin six times, what's the expected number of heads? And what's the chance of exactly three?

  4. What's the first date after today, written as a two-digit day, two-digit month and four-digit year, in which all eight digits are different?

  5. Next problem. You have an expensive function from integers to integers. I'd like a memoized version, so repeated calls with the same input come back fast. What's your plan?

  6. This runs in a long-lived process and the memory keeps growing. What's the problem, and how would you bound it?

  7. How do you make first-in, first-out eviction O(1)?

  8. Now switch to least-recently-used eviction. What's the simplest correct version, and what does it cost?

  9. Can you get every operation down to O(1)?

  10. Some fundamentals. Explain tail recursion, and why a compiler might care.

  11. Before we finish, put a confidence on each of the answers you've given me today.

  12. Before I roll, would you move your market now that you're short ten? Why or why not?

What a strong answer does

The questions above fall into 3 kinds. What a strong answer does differs by kind, not by question.

Technical9 of 12 above
State the intuition first; walk through the mechanics; make assumptions explicit; test a risk or edge case; connect the answer to the role.
Behavioral2 of 12 above
Lead with the claim and context; isolate your personal action and decision; explain the trade-off; quantify the result; finish with what you learned and changed.
Market1 of 12 above
State a view; support it with evidence and a catalyst; explain valuation or transmission; give the strongest countercase; name the risk that would change your mind.

92 more Jane Street questions

The rest of the bank — 104 in total — is asked by the interviewer during practice, so you meet them the way you would on the day rather than reading them first.

Practise Jane Street questions

How these questions were researched

Every question carries a provenance grade. Some were reported by candidates who sat the round, some come from the firm’s own published guidance or a source that trains for it, and the rest are written to match how this firm asks. Each seat is studied on its own — the round it actually runs, the order it runs it in, and what it is listening for. A Jane Street round is not a generic behavioural screen, and practising one as the other is how people walk in unprepared.

Falas is not affiliated with or endorsed by any employer named. Simulations are independent practice based on publicly described recruiting formats.