All topics
Math & probability
Mental Math & Estimation
Speed arithmetic, Fermi estimation, drills
Overview
About mental math & estimation questions in quant interviews
Speed arithmetic and Fermi estimation under time pressure — the format behind Optiver's 80-in-8 and the mental-math screens prop firms open with.
How to study this topic
A path that works
- 1
Start with the easy set
Warm up with the 15 easy mental math & estimation questions. Quick wins build pattern recognition before complexity ramps.
- 2
Drill the medium tier next
22 medium questions sit in the sweet spot where most interview questions cluster. Time yourself, then redo any you missed two days later.
- 3
Stress-test on hard problems
6 hard questions simulate the on-site round. Skip looking at solutions for at least 20 minutes, then write up your approach.
The library
All 43 mental math & estimation questions
easySymmetric Percentages: The Swap RuleeasyThe Gaussian SummationeasyRapid Fire: The Two-Digit SquareeasyThe Cube Root SprinteasyTriangular Matrix DeterminanteasyPercentage CalculationeasyQuick Square CalculationeasyScientific Notation SprinteasyThe Nines Divisibility CheckeasyThe Compound IllusioneasyThe Exponent DueleasyCompounding Estimation: The Rule of 72easyRadian ConversioneasyTax and Surcharge CalculationeasyThe Basis Point ConvertermediumThe Volatility AnnualizermediumEstimating Square Root of 10mediumMarket Sizing: The Golden ArchesmediumReciprocal of PrimesmediumCompounding vs. Linear: The 10-Year HorizonmediumVolatility Scaling: The Root of 50mediumBinary Scales: The Kilobyte ThresholdmediumApproximating with emediumApproximating Square Root of 2mediumMental Math: 18 x 22mediumThe Log LaddermediumThe Binomial Speed RoundmediumThe Natural Log ShortcutmediumThe Prime Reciprocal: SeventhsmediumThe Chunking MultipliermediumThe Factorial MagnitudemediumTaylor Quick DrawmediumNYSE Daily Trade EstimatemediumFermi: Cash MachinesmediumMonthly CompoundermediumBond Price Change EstimationmediumRapid Fire: Difference of SquareshardThe Harmonic Partial SumhardThe ATM Option ShortcuthardEstimating a ReciprocalhardStirling's Quick EstimatehardSizing the Market: The Piano Tuners of NYChardEstimating Pi with Leibniz Series
View all 43 mental math & estimation questionsRelated topics