Quant Interview Questions
A practical map of quant interview question types: probability, expected value, market making, mental math, estimation, statistics, and coding.
Students preparing for quant trading, research, developer, or internship interviews.
What quant interviews usually test
Quant interview questions cluster into six recurring families: probability and counting, expected value and fair pricing, statistics and inference, market making and trading games, mental math and estimation, and coding. Most first-round questions are short - two to ten minutes each - and the interviewer is scoring your model at least as much as your number. A strong answer names the sample space or state variable, picks the smallest method that fits (complement, symmetry, linearity of expectation, conditioning, or recursion), computes visibly, and checks the result against a bound you can state in one sentence.
Concrete example
Take "roll two dice, what is the chance the maximum is at least five." Counting the event directly means enumerating every pair containing a five or a six; counting the complement is faster. Both dice at most four gives 4 x 4 = 16 of 36 outcomes, so the answer is 1 - 16/36 = 20/36 = 5/9, about 0.556. Two checks confirm it: the answer must exceed the 1/3 chance that one specific die is at least five, and it must fall below 2/3, the union bound over the two dice. The same complement move generalizes: "at least one six in n rolls" is 1 - (5/6)^n.
How to practice
Practice by method, not by memorized puzzle. Keep separate buckets for coin and stopping problems, dice and counting, cards and sampling without replacement, Bayes and base rates, expected value and fair price, market making, and estimation - then run mixed sets once each method is reliable, because recognizing the method without being told the chapter is the skill the interview actually tests. After every miss, write the one sentence that would have found the method faster: "the hand is unordered, so the denominator is C(52,5)" beats "I should study cards more." The LeetQuidity calibration is a fast way to find which bucket is genuinely weak before you commit a month to the wrong one.
Common mistakes
The expensive mistakes are structural, not arithmetic. Candidates reach for a formula before defining the event; multiply probabilities that are not independent, using (4/52)^2 instead of (4/52) x (3/51) for two aces off the top of a deck; go silent so the interviewer cannot tell a slip from a broken model; or keep pushing after a hint instead of treating the hint as new information. Say what you are conditioning on out loud, and finish every answer with a bound or an edge case rather than a bare number.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.