Aptitude tests › Mental arithmetic
The mental arithmetic test: 80 questions in 8 minutes
Trading firms and market makers often start their hiring with a mental arithmetic test. A common shape is 80 short sums in 8 minutes, with no calculator and no paper: six seconds a question. The sums are school level: whole numbers, decimals, fractions and percentages. What the test measures is how fast and how accurately you do them under pressure, and most people don't finish.
What the questions look like
- Adding and subtracting: three-digit numbers, such as 874 − 441.
- Multiplying: a two-digit number by one digit at the start (61 × 3), then two digits by two (47 × 36), then three by two.
- Dividing: exact divisions, then divisions with decimals, such as 1.44 ÷ 0.12.
- Decimals and fractions: 0.3 × 1.2, a fraction as a decimal, a chain of fractions.
- Percentages: 35% of 240, or what percentage 18 is of 72.
For one firm's version, see the Optiver 80 in 8 page. Formats differ between firms. Some give options to choose from and some ask you to type the answer; some take a mark off for each wrong answer, so a guess can cost you. The invitation usually says which, so read it before you start.
Shortcuts that save seconds
- Split one factor: 47 × 36 = 47 × 30 + 47 × 6 = 1,410 + 282 = 1,692.
- Round and adjust: 49 × 36 = 50 × 36 − 36 = 1,764.
- Either side of a round number: 47 × 53 = 50² − 3² = 2,491.
- Times 11: 43 × 11 is 4, then 4 + 3, then 3: 473.
- 25 and 125 have partners: 76 × 25 = 76 ÷ 4 × 100 = 1,900.
- Decimals: multiply as whole numbers, then count the decimal places. 0.3 × 1.2 is 36 with two places: 0.36.
- Percentages: build them from 10%, 5% and 1%, and remember that x% of y is y% of x.
The quant interview maths guide has the full list, each with a worked example.
How to prepare
- Learn the shortcuts one at a time in untimed practice, until you reach for them without thinking.
- Then add the clock. Timed practice gives each sum a limit, and the level rises as you get them right.
- Skip what is slow. At six seconds a question, one stubborn sum costs you three easy ones.
- If wrong answers lose marks, don't guess blind. Answer what you can work out and leave the rest.
- Sit full-length runs before the real thing: 8 minutes of constant arithmetic is tiring in a way that short practice doesn't show.
Start now
Mental arithmetic practice here is free up to level 3, timed or untimed. The full run of 80 typed sums in 8 minutes, with a new set of questions each time and a result that shows right, wrong and right minus wrong, comes with paid access.