The $200K Guesstimate: Fermi Math for Tech, Consulting, Startup & Finance Interviews

By Adrian Keller

Big interview questions are rarely about finding one perfect number. They are about how you think when the data is incomplete.

The $200K Guesstimate teaches a practical framework for tackling Fermi and estimation questions across tech, consulting, startup, and finance interviews. Instead of memorizing famous answers, you learn a repeatable process:

DECOMPOSE → ANCHOR → SANITY-CHECK

Across 100 fully worked problems, you will practice how to break unfamiliar questions into manageable parts, choose defensible assumptions, keep units and orders of magnitude under control, stress-test uncertain inputs, and communicate your reasoning clearly under pressure.

Inside you will find:

- 100 worked estimation and interview problems
- Tech, consulting, startup/VC, quant, finance, and classic Fermi examples
- Step-by-step decomposition and sanity-check methods
- Mental-math and calibration techniques
- Sensitivity analysis and uncertainty handling
- Sample spoken answers and common traps
- A self-scoring rubric
- 2-week and 30-day practice plans
- Interview-day recovery and troubleshooting strategies

This is an interview-preparation book about structured reasoning-not a collection of numbers to memorize. The goal is to make your thinking visible, adaptable, and defensible when the answer is uncertain.

• Format: Paperback
• Language: English
• ISBN: B0HKC9X94P
• ISBN13: 9798175474467
• Release Date: September 2026
• Publisher: Independently Published
• Length: 112 Pages
• Weight: 0.35 lbs.
• Dimensions: 0.2" x 6.0" x 9.0"