Several trading firms gate their early rounds with a timed mental-arithmetic test, and it eliminates a large share of applicants before anyone reads a CV. The good news: it is a pure skill, and skills respond to deliberate practice.
What the test looks like
The most famous example is Optiver's "80 in 8" — widely reported as 80 arithmetic questions in 8 minutes, no calculator, with a penalty for wrong answers. That is roughly six seconds per question. Flow Traders uses a similarly fast multi-section arithmetic test as its main filter, while IMC's online assessment leans on timed cognitive and aptitude tests rather than an Optiver-style blitz. Formats shift year to year, so treat specific counts as commonly reported rather than guaranteed.
The arithmetic itself is not advanced — addition, subtraction, multiplication, and division over integers, decimals, and fractions. What is hard is doing it accurately at speed under pressure.
Techniques that buy you time
| Technique | Example |
|---|---|
| Percentages via fractions | 12.5% of 64 = 64 ÷ 8 = 8 |
| Break products apart | 14 × 23 = 14×20 + 14×3 = 322 |
| Use complements | 1000 − 367: count up to get 633 |
| Round, then correct | 49 × 6 = 50×6 − 6 = 294 |
| Multiply by 5 as ÷2 ×10 | 86 × 5 = 860 ÷ 2 = 430 |
Key insight. None of these are tricks for their own sake — each replaces a slow written algorithm with a faster path. Knowing your tables cold (including squares to 25 and the common fraction-to-decimal conversions) matters just as much: recall always beats calculation.
How to train
Speed comes from volume under a clock — there is no shortcut.
Watch out. Practise daily in short, intense bursts rather than occasional long sessions. The test rewards sustained accuracy at pace, so train that specifically; grinding slowly just builds the wrong habit.
NeetQuant's Mental Math Blitz reproduces the no-calculator, against-the-clock format, and the Number Box drill trains rapid column addition. For the pattern-recognition half of these batteries, see the sequence-tests guide. Build the habit weeks before you apply — by the firms' own framing, if you cannot clear the arithmetic filter, nothing else on your application gets seen.
After the arithmetic
Clearing the speed test gets you to the interesting rounds: probability, expected value, and market-making games. Start building that intuition in parallel — and if you are targeting a specific firm, the Optiver guide walks through its full process.