Quant Interview Prep

Quant interviews at hedge funds, trading firms, and quantitative finance desks are a different species from banking interviews. The questions are mathematical and fast. You will rarely be asked to walk through a valuation model or explain why you want the job. You will be asked to solve a probability puzzle in your head, under mild time pressure, while someone watches whether you panic or reason clearly.

The good news: the puzzles are not about obscure knowledge. They test whether you can think combinatorially, whether you understand conditional probability intuitively (not just formally), and whether you can set up a calculation cleanly before executing it. The most common failure is attempting computation before clarifying the setup — which produces confident but wrong answers.

The foundational tool is expected value. Every quant puzzle is ultimately an expected value question: given a set of outcomes and probabilities, what is the fair price of a bet, the expected waiting time, or the probability that a particular sequence occurs? The second most important tool is Bayes' theorem: how do you update a probability given new information? These two concepts, combined with the ability to condition on events and use symmetry arguments, handle the vast majority of first-round quant interview questions.

Comfort here signals to an interviewer that you can think in probability — the language of every trading decision.