Quant Interview Arithmetic Without a Calculator
How to do quant interview arithmetic without a calculator using decomposition, benchmarks, scratch work, approximation, and error checks.
Candidates who rely too much on calculator-style computation.
Use decomposition
Break calculations into parts you can hold mentally. This is usually more reliable than imitating written long arithmetic in your head.
Use scratch work
Calculator-free does not mean scratch-free. Write intermediate values, units, and denominators when the calculation has multiple steps.
Concrete example
For 23 percent of 400, compute 20 percent as 80 and 3 percent as 12. The result is 92, with an easy check near one quarter of 400.
Approximate deliberately
If the decision only needs scale, say you are approximating. If the threshold is close, do the exact arithmetic before deciding.
Common mistakes
Candidates often try to keep every number in memory. Good scratch work is part of strong mental math, not a weakness or a failure of speed.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.