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Demo case file · Technical

Jane Street

Trader

Finance Technical Hard 60 min

This is a demo case file: a realistic example written from commonly known interview formats, not a real candidate's interview experience.

Questions asked

  1. You flip a fair coin until you get two heads in a row. What is the expected number of flips?
  2. Make me a two-sided market on the number of piano tuners in New York City.
  3. I just sold to you at your offer. Does that change your view? Update your market.

What to expect

Mental math and probability throughout, then a market-making game where the interviewer actually traded against my prices. They cared more about how I updated on new information and sized my confidence than about any single right answer. Saying "I'm not sure, here's my reasoning" went down well.

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