How to Prepare for the Optiver Mental Math Test

The Optiver mental math test — 80 arithmetic questions in 8 minutes — is a first-round filter for one of the most competitive prop trading firms in the world. Pass it and you're in the mix. Fail it and the door closes before it opens.

Here's what the test actually covers, and a systematic way to prepare.

What the Test Looks Like

The 80-in-8 is pure speed arithmetic:

• Addition and subtraction of 3–4 digit numbers
• Multiplication of 2–3 digit numbers
• Division with remainders or decimals
• Percentage calculations (e.g. "What is 17.5% of 240?")
• Fractions and ratios

There are no word problems, no logic puzzles, no finance knowledge required. You need to process one problem every 6 seconds with >85% accuracy.

Why It's Hard

The arithmetic itself is not hard. The challenge is the pressure and pace. At 6 seconds per question, you can't verify your work. You commit and move on.

Most candidates who fail do so not because they can't do the math — but because they freeze under time pressure, or because they've only ever done math with a calculator.

The Right Practice Approach

1. Build Your Shortcuts First

Before drilling speed, internalize these:

Multiplication shortcuts:

• Multiply by 9: multiply by 10, subtract original (37 × 9 = 370 − 37 = 333)
• Multiply by 11: add the two digits and insert in middle (53 × 11 = 5[5+3]3 = 583)
• Multiply by 25: divide by 4, multiply by 100 (48 × 25 = 12 × 100 = 1,200)
• Near-100s: (98 × 97) = (98−3)(100−2) pattern

Percentage shortcuts:

• 1% of X = X/100
• 15% = 10% + 5% (half of 10%)
• 12.5% = 1/8
• 33.3% ≈ 1/3

2. Daily Timed Drills

Practice with actual time pressure. Aim for 60-second sprints where you answer as many problems as possible. Track your count — if you're hitting 12–15 correct in 60 seconds, you're in range for the 8-minute format.

Fermiq's blitz mode gives you 60-second timed runs with instant feedback. The Math and Probability categories are most relevant.

3. Estimation Over Perfection

Optiver's test has a generous but not unlimited tolerance. A 2% error on a multiplication is usually fine. A 30% error is not.

Practice rounding to the nearest friendly number and then correcting:

• 247 × 38 → 250 × 38 = 9,500, then subtract 3 × 38 = 114 → 9,386

4. Simulate the Pressure

Don't just practice the math. Practice under simulated stress:

• Set a 8-minute timer, give yourself exactly 80 problems
• Do it in the morning before coffee
• Do it after a stressful situation

The point is to build the reflex of committing to an answer quickly, not agonizing over it.

What Score Do You Need?

Optiver typically uses 60+ correct as the pass threshold (75%+ accuracy), but this varies. Candidates report the test rejecting anyone below ~55 correct.

Top candidates complete 70–80 questions correctly.

Resources

• Fermiq blitz mode — 60-second timed sprints with Elo tracking
• Fermiq interview prep curriculum — structured 6-week prep path
• Mental math guides — shortcuts and reference formulas

The test is beatable. Most quant roles at Optiver, Jane Street, SIG, and similar firms use variants of this format. Build the reflex once and it transfers everywhere.