Quant Developer Interview Questions

2,954 quant developer interview questions shared by candidates

You are given three envelopes, one of which contains $100 and the others contain nothing. You randomly pick one envelope but don’t open it. The interviewer then opens one of the other two envelopes and shows that it’s empty. Now you have a choice: stick with your original envelope or switch to the other unopened envelope. What should you do to maximize your chances of winning, and why?
avatar

Quant Trader Intern

Interviewed at Jane Street

4.4
Oct 17, 2024

You are given three envelopes, one of which contains $100 and the others contain nothing. You randomly pick one envelope but don’t open it. The interviewer then opens one of the other two envelopes and shows that it’s empty. Now you have a choice: stick with your original envelope or switch to the other unopened envelope. What should you do to maximize your chances of winning, and why?

You play a 100-round game: each round you can either roll a fair 20-sided die (uniform 1 to 20) or “lock in” the current face and collect that same reward for all remaining rounds. You must roll in the first round. What is your optimal stopping / locking strategy and expected value?
avatar

Quant Trading Intern

Interviewed at Jane Street

4.4
Sep 30, 2025

You play a 100-round game: each round you can either roll a fair 20-sided die (uniform 1 to 20) or “lock in” the current face and collect that same reward for all remaining rounds. You must roll in the first round. What is your optimal stopping / locking strategy and expected value?

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