Jane Street Interview Questions
The real Jane Street quant-interview problems candidates report — probability, expected value and combinatorics — each with a full worked solution.
Inside the Jane Street interview
Jane Street is a quantitative trading firm (and famously an OCaml shop) known for interviews run as a live probability conversation rather than a coding gauntlet. The set leans heavily on probability and expected value, with combinatorics, light game theory, and a smaller coding strand alongside.
What they test
By far the biggest blocks are probability and expectation — together more than half the set: fair-value of a game, conditional and Bayesian updates, optimal-stopping and dice/coin puzzles. Around them sit combinatorics (counting arrangements, paths, and symmetric cases), a thread of game theory (betting, bidding, and adversarial play), and a handful of coding and brain-teaser questions to round things out.
The recurring shapes
Most prompts ask for a single number — an expected value or a fair price — and the work is condition on the first step, exploit symmetry, and sum over outcomes weighted by their probability. Expect to be pushed to commit to a number and then defend or revise it as the interviewer adds information.
How to approach
Think out loud and treat it as a dialogue — Jane Street cares how you reason under uncertainty, not just the final answer. Lean on linearity of expectation and symmetry before grinding algebra, set up a recursion or condition on the first event for the stopping problems, and sanity-check against small cases and extreme limits. State your assumptions and quote a price you'd actually be willing to trade on.
The mix is fairly balanced — 34 easy, 41 medium, 25 hard — so warm up on the quick fair-value puzzles, then build stamina for the harder multi-step expectation and game-theory questions.
Jane Street probability questions (30)
- Limiting Probability of the Last Die Face
- Monty Hall With Envelopes
- Probability a Three-Legged Disk Table Stands
- Maximize Red Marble Probability with Two Drawers
- Probability of Meeting at Office Hours
- Simulate a 10-Sided Die from a 6-Sided Die
- Fair Dice Comparison: d20 vs. 3d6
- Hitting a Fixed Target with a Growing Die
- Royal Firsts: One of Each Before the Ace
- Weekend Rain Bounds via Frechet-Hoeffding
- Marginal Distribution of a Beta-Binomial Mixture
- Probability a Selected Card Is Blue Given Its Value Is 1
- Race to Three Heads
- Russian Roulette Survival Probability
- Posterior Probability with Symmetric Urns
- Bayesian Die Identification
- Strictly Increasing Dice Rolls
- Even Heads with Mixed Fair and Unfair Coins
- Probability Three Dice Sum to Ten
- Probability of Three of a Kind in a 5-Card Hand
- Race to Four of a Kind
- Probability of One Car in Five Minutes
- Break-Even Price of a Digital with Two Independent Signals
- How Many Green Gloves in the Box?
- Matching Socks from a Drawer
- Probability That Two Random Primes Sum to an Odd Number
- Stock Returning to Its Original Price
- Odd Die, Even Result After Subtraction
- Coin Flip Probabilities: One, Two, and n Coins
- Probability It Rains Both Days
Jane Street expected value questions (26)
- Expected Number of Fixed Points in a Random Permutation
- Long-Run Win Proportion in a Serve-Switching Game
- Expected Minimum Ball in a Shared Bin
- Expected Rolls to See Each Die Face Twice
- Expected Value of the Running Total When It First Exceeds 100
- Place or Take: Two-Box Optimal Stopping
- Batch Coupon Collector Expected Coverage Time
- Optimal Coin Pair Reflipping
- Optimal Sample Size Before a Directional Bet
- Optional Stopping and the Doubling Strategy
- Expected Length of the Longer Piece
- Expected Total Payment in a Dice Rolling Game
- Expected Flips for Two Consecutive Identical Outcomes
- Expected Flips to Get k Heads
- Expected Length of the First Run
- Expected Rolls for a Consecutive 4-5 Sequence
- Expected Wait for a Periodic Ferry
- Expected Draws to Get a Matching Pair of Socks
- Single Die vs. Average of Two Dice
- Bayesian Posterior and Break-Even Price Under Information Asymmetry
- Correlation-Robust Expected Value Bounds
- Extreme-Value Trading Threshold
- Marathon Runner With and Against the Wind
- Expected Drive Time with Stoplights
- Pool Filling Rate with Two Hoses and an Open Drain
- Card Draw With Reservation Value
Jane Street combinatorics questions (17)
- Uniform Sum Distribution With Relabeled Dice
- Recover Individual Watermelon Weights from Pairwise Sums
- Finding the Top Three Horses in Minimum Races
- Sums of Fours and Fives
- Arithmetic Progression-Free Sequence Completion
- Guaranteed Birth Month Match: Pigeonhole Principle
- Counting Wins in Rock-Paper-Scissors
- Minimum Number of Drainers at a Concert
- Counting Digit Occurrences in a Range
- Counting Sub-Cubes Inside a Cube
- Dividing Students into Labeled Groups
- Guest List with Exclusion Constraint
- Largest Five-Digit Number With Distinct Pairwise Digit Sums
- Matchy Palindromes
- Monotone Signaling via Breaking Glass
- Smallest Integer with Digit Product 96
- Counting Even-Length Palindromes
Jane Street game theory questions (8)
- Lions and Gazelle: Backward Induction
- Three-Way Duel With Rational Players
- Ultimatum Game: Optimal Split Proposal
- Choose Your Map Selection Method
- First-Price Auction: Equilibrium and Optimal Reserve
- Penney's Game with Biased Coin
- ABA vs. BAB Tournament Sequence Strategy
- Restricted Rock-Paper-Scissors Nash Equilibrium
Jane Street coding questions (7)
- Misra-Gries Heavy Hitters Algorithm
- Reservoir Sampling from an Unknown-Length Stream
- Minimum Number of Rooms for Interval Partitioning
- Longest Subarray With Sum at Most K
- Longest Substring with at Most K Distinct Characters
- K Smallest Pair Sums from Two Sorted Arrays
- Online Mean and Variance with Exponential Forgetting
Jane Street brain teasers questions (5)
Jane Street optimization questions (3)
Jane Street finance questions (1)
Jane Street regression questions (1)
Jane Street market microstructure questions (1)
Jane Street statistics questions (1)
Jane Street interview FAQ
What kind of questions does Jane Street ask in quant interviews?
Candidates most often report probability, expected value and combinatorics questions. This page collects 100 of them, 14 stamped with the month they were last reported — each with a full worked solution.
How hard are Jane Street interview questions?
The set spans 34 easy, 41 medium and 25 hard problems. Most sit at medium difficulty — solvable in a few minutes with clean reasoning — with a harder tail that rewards knowing the canonical tricks.
How do I prepare for the Jane Street quant interview?
Work through this set by topic (use the sidebar), starting from your weakest area. 26 problems are free to open with their full solution, so you can judge the quality before anything else. Then walk the full Jane Street interview guide for the round-by-round funnel and the online assessment.
Are these the actual Jane Street interview questions?
They are built from candidate-reported Jane Street questions. We rewrite each prompt for clarity and author the worked solutions ourselves — we don't claim the wording is verbatim, and we never invent questions or recycle generic lists. 14 of 100 carry the month they were last reported.