Jane Street
A proprietary trading firm known for hiring on raw reasoning rather than finance background.
What the rounds test
- Mental arithmetic at speed
- Probability and expected value
- Market making and betting games
Firms in this mould interview for how you handle uncertainty out loud: quoting a two-sided price, updating it when information arrives, and saying how confident you are without being asked. Preparation that only covers closed-form problems tends to under-serve this.