Prep by Firm

Jane Street interview prep: reason out loud, price everything

No finance knowledge expected and no coding for traders. The Jane Street funnel is probability, expected value and making markets on partial information, and they grade the reasoning you narrate, not just the answer. Each stage has a matching drill here, free.

Open the Jane Street training plan Practice puzzles out loud

What the Jane Street process tests

A timed mental-math screen: 60 questions in 8 minutes across multiplication, division, percentages and decimals. The bar is accuracy, roughly 70 to 80 percent.
Phone rounds: 3 to 5 probability and game-theory puzzles, reasoned out loud (coins, dice, cards, expected value).
Trading games: make a market on a hidden quantity, often cards, then update and tighten as information is revealed.
Estimation: questions that ask for a confidence interval you would actually bet on.
Behavioral: light; the constant across every round is thinking out loud and catching your own errors.

Warm up on the real thing

Make a market on the sum of two dice rolls.

Fair value 7. Quote around it, say 6.8 bid at 7.2 ask, and be ready to move: if the interviewer lifts your offer instantly and asks for size, ask yourself what they know that you priced wrong. The game is updating, not the first number.

The first card off a shuffled deck is an ace. What is the chance the second one is too?

3/51 = 1/17. Say the conditioning out loud: 3 aces left among 51 cards. Clean narration of a one-line argument beats a silent correct answer here.

Give a 90% confidence interval for the takeoff weight of a fully loaded Boeing 747.

Something like 250 to 500 tonnes. (The maximum takeoff weight is about 400 tonnes.) The trap is quoting a range that is too narrow: they are testing calibration, whether your 90% intervals contain the truth 90% of the time, not precision.

A ready-made training plan

The app's Prep by Firm desk has a Jane Street card that maps their funnel onto the right drills and launches each in one click: an 8-minute timed arithmetic run at their accuracy-first pace, a probability study set spanning classics, expected value, coins, dice, cards and game theory, multi-step brainteasers with an AI examiner that probes your reasoning the way a phone interviewer would, the market-making arena, the Fermi estimation lab for interval calibration, and a full timed interview simulation to rehearse narrating under pressure.

Start the Jane Street plan free

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Explore the rest of the desk

Brainteasers67 classic puzzles with an AI examiner Probability Lab285 interview questions with worked solutions Market Maker ArenaQuote two-sided markets against informed flow Fermi Lab80 estimation problems scored on order of magnitude

Based on public interview reports and candidate accounts; formats change, so verify the current process with your recruiter. My Quant Journey is independent: not affiliated with, sponsored by or endorsed by Jane Street.