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Estimation / guesstimates

Reason to a number.

Case

Overview

Estimation (Fermi) questions ask you to size an unknown quantity from first principles. Interviewers watch your structure and assumptions, not the exact number — decompose, justify, and sanity-check.

How it works

Case
ClarifyDecomposeAssumeComputeScopeunitFactorspop × rateReasonable~Answer
ClientServiceEdgeData

Step by step, with examples

  1. 1

    Scope

    • Define exactly what to size.
  2. 2

    Factors

    • Break it into drivers.
  3. 3

    Reasonable

    • State each assumption.
  4. 4

    Answer

    • Sanity-check the magnitude.
    • Example: gas stations in a city

Overview

Decompose into drivers, state assumptions out loud, compute, and sanity-check the magnitude.

Common pitfalls

  • Guessing without structure
  • Hidden assumptions
  • No sanity check

Where this content comes from

For full transparency, this content is curated and verified from these sources:

Behavioral interview frameworks (STAR/CAR)Consulting case-interview casebooksOppZen-authored communication playbooks