Most people train backwards.
One-on-one quant interview preparation with a theoretical physicist. You don't need another two hundred solved problems — you need a different way of looking at them.
Prepare for the firms that filter hardest
The process is broadly the same everywhere: an online assessment, a mental-math round, brainteasers, a market-making game, then people who want to watch you think. We train the whole pipeline.
What we actually train
Not a content library. A weekly hour where someone watches how you think and tells you what you did wrong — which is the one thing no platform, book or problem set can do for you.
Perception under pressure
What happens in the two seconds before the solution. How to look at a problem you have never seen, and what to do when you don't know what to do.
Probability & expected value
Conditioning, base rates, Bayesian updating and calibration — trained as instincts you can reach for at a whiteboard, not as formulas you recite.
Mental math & estimation
Speed and accuracy under a clock, plus Fermi estimation, orders of magnitude and knowing the moment when approximating beats computing.
Brainteasers you've not seen
Symmetry, invariance, conservation and dimensional constraints — the structural patterns a physicist builds after a thousand problems, taught directly.
Market making games
Quoting a two-sided market, managing exposure, and staying coherent while someone deliberately trades against you and asks why.
How markets actually work
Bid, ask, spread, quoting obligations, rebates, latency. The context most candidates skip — and the one interviewers use to separate the serious.
Online assessments
Sequence tests, numerical reasoning and the timed cognitive rounds that knock people out before a human has read a single line of their CV.
Non-quant routes
TPM, operations and adjacent roles at trading firms. Different interview, same market knowledge — and far less competition than the trader pipeline.
02 / THE THESIS
Solve it. Then rewind your own thinking.
People grind the Green Book, Heard on the Street and Brainstellar, memorise two hundred solutions, walk into an interview, get a problem that is slightly different — and lock up. They are rarely dumb. They trained the wrong thing.
Find the minimal observation
Every puzzle turns on one move. Blindfolded, a hundred coins, thirty heads up — the answer is not combinatorics, it's realising you can flip. We train the question that gets you there.
Rewind your own thinking
After every problem, solved or not: which observation cracked it open? This is as much self-analysis as problem analysis, and it is why it takes real time.
Build a library of structure
Grandmasters don't calculate twenty moves ahead — they see the board differently. Symmetry, conservation, invariance. Perception, and it is trainable.
03 / START HERE
What to read, and how
These three are free or close to it, and they are what I actually work from. The order matters less than the habit: one problem a day, then ask what the minimal observation was.
Street-Fighting Mathematics
Dimensional analysis, symmetry and approximation. It won't teach you finance — it will teach you to see through a problem. G.I. Taylor deduced the yield of an atomic bomb from a single photograph this way.
50 Challenging Problems in Probability
One problem per day. Not five, not twenty. The point is the analysis afterwards, and you cannot do that properly on volume.
STAT 110
Free lectures. Don't watch for the syllabus — absorb the way Blitzstein thinks about probability. That framing is the transferable part.
04 / TRY IT NOW
The problem this place is named after
A student had been at this for twenty minutes with combinatorics. One question unstuck her, and it took ten seconds. Try it before you open the answer.
You are blindfolded. In front of you are 100 coins, exactly 30 of them heads up. You may touch and move the coins, but you cannot feel which way any coin faces. Separate them into two groups with an equal number of heads.
Show the observation
The unsticking question: forget counting — what operation links two groups mechanically?
The move: take any 30 coins and turn every one of them over.
Why it works: say your pile of 30 contains h heads. The other 70 coins must then hold 30 − h heads. Turn your 30 over and your h heads become tails while your 30 − h tails become heads — leaving exactly 30 − h heads in each pile. It holds for every value of h. No probability, no combinatorics, and it is guaranteed rather than merely likely.
Note what the work actually was. Not calculation — noticing that turning a coin over is the operation that couples the two piles. That noticing is the thing we train, and it is what this place is named after: thirty heads, and the move that makes counting them unnecessary.
05 / FROM THE THREAD
The questions people actually sent
Verbatim, from the AMA and the direct messages that followed it. If one of these is yours, that is exactly what the first session is for.
“I have now bombed 2 really pivotal interviews due to my not knowing how to problem solve without iterating several times.”
Post-grad, breaking into buyside“What's the one thing you'd tell someone to practice daily at home to start building that kind of pattern recognition? Not a specific problem type, more like a mindset or habit.”
r/FinancialCareers“I'm running into issues understanding the logistics of the scenario rather than the actual logic. Does this ameliorate over time?”
Working through Mosteller and the Green Book“For people coming from non-quant finance roles, is it realistic to transition into quant later, or is the door basically closed without a math/CS background?”
Capital markets“In your honest opinion, do you think intelligence determines one's ability to break into quant?”
r/FinancialCareers“If you could start from scratch in terms of dedicated interview prep, what would be your process?”
Undergraduate“Do you do tutoring for product management roles in quant firms, like Jane Street's TPM role?”
Direct message“Do you have a website or something where you advertise your services?”
Former high-level chess player“Are there beginner-friendly resources for high school students? Is it too early to think about preparing for MFE/quant internships?”
Student“What's the best way for someone coming out of IB to position themselves in recruiting for quant roles?”
Investment banking06 / THE FIRST STEP
Fifteen minutes, free, no pitch
A conversation, not a test. You tell me where you are, what you have already tried and where you are trying to get to. I tell you honestly whether I can help — and if I can't, I'll say so and point you somewhere better.
You talk, I listen
Which firms, which stage, what has gone wrong so far, how long you have. Nothing to prepare and nothing to bring.
An honest read
What I think is actually standing between you and the offer, and what I would do about it — including the version where you do it alone.
An interview
You will not be put on the spot or asked to solve anything. No script, no slide deck, no follow-up sequence afterwards.
Tell me where you're stuck.
Fifteen minutes over Meet or Discord. You talk about where you are and where you want to be; I tell you straight whether I'm the person to get you there.
Book the free 15 minutes →07 / QUESTIONS
Straight answers
Do I need a maths or CS degree?
No, and this is the question I get most from people in capital markets, corporate finance and IB. Perception is trainable independently of your transcript. What a degree buys you is a screening advantage, not an interview advantage — and there are adjacent routes into these firms (TPM, operations, risk) that most candidates never even look at.
Am I clever enough for this?
Almost certainly. In several years of doing this, the people who failed were rarely the ones lacking horsepower — they locked up. As one of my professors put it: you are lucky if you keep half of your IQ when you walk up to the board. That gap is the trainable part, and it is where nearly all of the improvement lives.
I'm already grinding the Green Book. Isn't that enough?
It's necessary and it isn't sufficient. The question is not what you are solving, it's what you do in the ten minutes after. If you cannot say which observation cracked a problem open, you have added a solution to your memory and nothing to your perception — which is why a slightly unfamiliar problem still ends you.
Why not just buy a drilling platform for €40 a month?
Buy one, genuinely — they are good at what they do. A platform measures your output: right, wrong, how fast. It cannot tell you that you missed a symmetry, reached for combinatorics when you should have reached for an invariant, or went quiet at the exact moment you should have thought out loud. That diagnosis is the thing being sold here.
Is it too early? Is it too late?
Both questions get asked, and the answer to both is usually no. High school is not too early — pattern recognition compounds over years and you have the rarest thing, which is time. And people move into these firms from other careers regularly; the door is narrower, not shut.
What actually happens in a session?
You get a problem. You work on it for a few minutes while I stay out of the way. Then we sit down over it together and I ask what you were looking at. Ten to fifteen rounds of that in an hour. It is deliberately uncomfortable, because the interview will be too.
How much time do I need between sessions?
One problem a day from Mosteller, plus the analysis afterwards. That is the whole volume. People who do three hours a night and skip the analysis progress more slowly than people who do twenty minutes and do it properly.
What does it cost?
The first fifteen minutes are free. After that sessions run a little under $200 for an hour, usually weekly, over Meet or Discord. There is no package you have to commit to up front and no minimum number of sessions — people tend to stay until their interviews are done, and then they stop.
Do you cover non-trading roles?
Yes, and it is one of the more useful things I do. Technical program management, operations and risk at trading firms are a real route in and a far less crowded one than the trader pipeline — people arrive there from big-tech product roles, from engineering, from consulting. The work is different from trader prep: recruiter screens, the market knowledge a non-trader is still expected to have, and getting the “why leave, why a trading firm” answer to sound pull-motivated rather than push-motivated, which is usually what decides those conversations.