September 01, 2026 | Read online | How much would it cost to clean every window in London? Logic questions for PMs, engineers, and data analysts |
|  | | Sophie @ the stack |
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| | 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. | | | | | | | TECHNICAL INTERVIEWS | | 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?” | | 👇 Prefer a video? Keep scrolling to watch a full breakdown. |
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| | | | | ANSWER TECHNIQUE |  | How To Answer Estimation Questions Like A Product Manager |
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| 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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