How much would it cost to clean every window in London?

Logic questions for PMs, engineers, and data analysts Sophie @ the stack September 01, 2026 Your weekly advantage in the global tech job market. New here? Join 55,000 engineers getting hired at Amazon, Meta and Revolut. Sign up now .

Logic questions for PMs, engineers, and data analysts

Sophie @ the stack September 01, 2026

Your weekly advantage in the global tech job market.

New here?** Join 55,000 engineers getting hired at Amazon, Meta and Revolut. Sign up now .

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In 2017, I had just finished university and started interviewing for graduate Data Analyst roles.

This was the first time I was asked a logic question: “How much would it cost to clean all the windows in London?”

At first, I was confused. How is this related to data analysis at an insurance company?

Turns out, it's a Fermi estimation question — common in interviews for product managers, data analysts, and any role that needs you to think logically under pressure.

" I have no idea, I've never even been to London " is the wrong answer.

So is immediately saying, “ err £5 million? ”

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GET EARLY ACCESS → ANSWER TECHNIQUE

3 tips for answering logic questions:

Estimate via proxy. Use related and known numbers

- Upper and lower bounds. What are the extremes? This gives you a range to work with.

- Personal references. Use your own experience to make an educated guess.

Read more on answering logic questions in interviews

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Source: The Stack newsletter — <a href="https://www.trythestack.co/p/how-much-would-it-cost-to-clean-every-window-in-london">original issue</a>.