Mental arithmetic practice for trading applications
Official sources reviewed Oct 18, 2026 and linked below. FBO practice suggestions are independent teaching material; your employer's current instructions take priority.
Build a reliable method for percentages, products and fractions. These are general practice exercises, not an official Optiver test specification or a promised route past a cut-off.
Confirm the assessment before you practise
Optiver Europe's recruitment FAQ provides assessment support and a route to request adjustments. It does not substantiate a universal mental-arithmetic question count, time limit or pass mark. Use the instructions supplied for your role and location.
The examples below are FBO arithmetic practice. They do not establish which topics you will receive, whether a calculator is permitted, or how unanswered and incorrect responses are scored.
Percentages: break the calculation into parts
For 15% of 80, calculate 10% first (8), then half of that (4), and add them to get 12. Try related values and check your result before trying to increase speed.
Products: use a nearby round number
For 87 × 8, use 90 × 8 − 3 × 8 = 720 − 24 = 696. Practise explaining the adjustment so you do not accidentally add when you should subtract.
Fractions: simplify first
For 3/8 × 64, divide 64 by 8 and then multiply by 3 to get 24. For 5/16 × 96, divide 96 by 16 and multiply by 5 to get 30. These examples can both be solved directly as fractions; converting to decimals is optional.
Check the result and the rules
Use an estimate to spot a misplaced decimal or implausible result, then calculate to the precision the question requires. Do not assume guessing is beneficial: follow the actual test's scoring instructions.
Keep an error log and practise the operations that cause mistakes. Improve speed after you can apply the method accurately; no practice score here guarantees a hiring outcome.