Mental Math Scratch Work Guide
Mental math scratch work guide for organizing expressions, intermediate values, units, checks, and corrections in quant interviews.
Candidates whose arithmetic notes become messy during interviews.
Write the expression first
Before computing, write what you are computing. This prevents stale numbers and makes corrections easier when the interviewer changes the prompt.
Keep units visible
Write percent, dollars, years, users, or probability next to values when units can be confused. Unit mistakes are common in estimation and EV prompts.
Concrete layout
Use three lines: setup, arithmetic, check. For EV, that might be outcomes and probabilities, weighted sum, then sign and scale check.
Mark corrections
If you revise a number, cross it out or restate it clearly. Do not leave two conflicting values on the board or in the spoken answer.
Common mistakes
Candidates often write calculations but not meaning. Scratch work should preserve both the number and what it represents.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.