PRACTICE GUIDE FLOW TRADERS
Flow Traders Probability & Estimation Practice Test
Flow Traders does not publish the shape of its probability & estimation screen, and candidates describe it as 10 to 20 questions in 15 to 45 minutes, roughly one to three minutes per question, answered by picking one of the options.
Those are ranges across firms running this format rather than Flow Traders's own figures, so treat them as the shape to train against and check the instruction screen on the day for the marking rule.
Outcry is not affiliated with Flow Traders and has no access to their assessment content. This guide describes an assessment format that candidates report publicly; the questions here are generated by Outcry and are not Flow Traders’s own.
What it screens
A liquidity provider specialising in ETFs, with offices in Amsterdam, New York, Cluj, Hong Kong and Singapore.
- ✓Expected value computed fast and used to make a decision
- ✓Conditional probability and Bayes updates without formal notation
- ✓Ranking likelihoods rather than computing them exactly
- ✓Fermi estimation: decomposing an impossible question into three easy ones
Where it sits at Flow Traders
A liquidity provider specialising in ETFs, with offices in Amsterdam, New York, Cluj, Hong Kong and Singapore. What that means for the screen is that the questions tend to be drawn from the work rather than from a textbook, so the format below is the shape to train against rather than a syllabus.
Candidates also report 3 other screens at Flow Traders, covered separately on this site. Where a firm runs several, they usually sit in one round rather than spread across the process, so the pacing of the whole set matters more than any single section.
The format
Flow Traders does not publish this screen's shape, and it varies between firms, so these are the ranges candidates report rather than exact figures.
| Questions | 10 to 20 |
|---|---|
| Time | 15 to 45 minutes |
| Per question | one to three minutes |
| Negative marking | Varies by firm and year |
| Answer style | Multiple choice or a typed number |
| Where it sits | First round, or a second technical screen |
What it tests, with a worked example
Every example below is generated by Outcry, drawn from the same question generators the timed drills run. None of them is Flow Traders’s.
Expected value and odds
Pricing a bet, converting between odds and probabilities, and deciding whether to take it.
Example
You roll a fair die 3 times. Probability of at least one six?
- 50%
- 32.1%
- 42.1%
- 0.5%
Answer 42.1%
Complement: 1 − (5/6)^3 = 42.1%. Adding 1/6 each time double-counts.
Conditional probability
Bayes' rule in disguise: a test result, a signal, a drawn card, and what it implies.
Example
A strategy's daily returns over n days average x̄ with sample standard deviation s. Which statistic tests whether the true mean return is zero?
- x̄ / (s/√n)
- x̄·√n / s²
- (x̄ − s) / n
- x̄ / s
Answer x̄ / (s/√n)
The one-sample t-statistic divides the observed mean by its standard error s/√n. Dividing by s alone ignores how the estimate sharpens with n.
Estimation under uncertainty
A number nobody knows exactly, reasoned to the right order of magnitude out loud.
Example
4 crates arrive at a receiving dock holding spacers, shims, gaskets and bolts, one content each. Each crate carries a label naming one of those 4 contents, no two labels the same, and every label is on the wrong crate. Opening a crate shows what is in it. How many crates must be opened, in the worst case, to relabel all 4 correctly?
Answer 2
The label-to-contents map is a permutation with no fixed point, and there are 9 of those on 4 items. Opening a crate reveals its contents and splits the live set; picking the next crate after seeing the last result, a minimax search over every opening order gives 2 as the worst case. With 4 = 3 the two possible arrangements are the two rotations, and one look separates them. The general pattern: the last two crates settle themselves only when the two contents left both clash with their own labels.
Ranking outcomes
Ordering several events by likelihood, where only the exact order scores.
Example
An index fund charges 5 basis points a year and keeps 3.0% of assets in non-interest-bearing cash. The index returns 6.0% over the year. What is the tracking difference in basis points, as a signed number?
Answer -23
Tracking difference is the fund's return less the index's. The invested 97.0% earns the index return and the cash earns nothing, so the drag is 3.0% x 6.0% = 0.1800%, or 18.00 basis points. The fee takes another 5 basis points. Together the fund returns 6.0% - 0.05% - 0.1800% = 5.7700%, a tracking difference of -23.00 basis points. Cash drag hurts in a rising market and the fee is the only part that costs the same whatever the market does. Tracking difference is the realised gap; tracking ERROR is the volatility of that gap and is a different number.
Symmetry arguments
Questions that collapse to one line once you notice the two cases are mirror images.
Example
A fair coin is flipped 4 times. What is the chance every flip is heads, as a percentage?
Answer 6.25
(1/2)^4 = 1/16 = 0.063, or 6.25%.
Reading the question exactly
At least, exactly, and given that - the three phrases that change the answer entirely.
Example
A puts in 3,000 for 4 months and B puts in 13,000 for 9 months. They clear 33,000 of profit. What is A's share?
- 16,500
- 10,153.85
- 6,187.5
- 3,069.77
Answer 3,069.77
Profit follows capital multiplied by time. A contributes 3,000 x 4 = 12,000 and B contributes 13,000 x 9 = 117,000, so A takes 12,000 / 129,000 of 33,000 = 3,069.77.
What a good score looks like
Probability rounds are usually marked as part of a wider battery, so a standalone threshold is rarely reported. Where candidates do describe one it clusters around getting two thirds of the items right, with the caveat that these sections are short enough that two mistakes move you a long way.
How to train for it
- 01Work the standard results until they are recall, not derivation: complement, conditional, binomial mean and variance, geometric expectation.
- 02Practise setting up before calculating. Most wrong answers on these are a correct calculation of the wrong quantity.
- 03Work the complement first whenever the question says at least or at most. It is usually the shorter route and it is almost always the intended one.
TRAIN IT HERE
The drills that match each section
Likelihood Ranking
Order events from most to least likely - the exact screen-question format.
Fermi Estimation
Piano tuners in Chicago, atoms in a body - scored on order of magnitude.
Quitters Never Lose
A casino stopping-strategy game that is secretly a martingale lesson.
Tail Risk
Rare events and fat tails, and what they do to a plain expected-value estimate.
SIT THE FULL BATTERY
All the sections back to back on one clock, marked the way the real screen marks them, with a by-skill breakdown at the end. Included with any pass.
Also reported at Flow Traders
Common questions
- Is the Flow Traders probability & estimation test multiple choice?
- Reported as multiple choice or a typed number. Formats move, so treat this as the shape rather than a guarantee.
- How long is the Flow Traders probability & estimation test?
- Candidates report 10 to 20 questions in 15 to 45 minutes, roughly one to three minutes per question.
- Is there negative marking on the Flow Traders probability & estimation test?
- It varies by firm and by year. Where a paper does mark negatively, skipping beats guessing; where it does not, answer everything. Check the instruction screen before you start - it is always stated there.
- How do I practise for it free?
- Every drill linked on this page is free to play, with no account, inside a daily run cap. Questions are generated fresh each run, so there is nothing to memorise between attempts.
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