I remember that once i had a job interview where things were going well, and then came the last question — the kind that really sticks with you.
The interviewer leaned back and asked,"So, how many windows are there in Berlin?"
Caught off guard, I looked at them and asked, “Windows like Windows vs Mac, or windows like doors and windows?”
They laughed and clarified, “Windows like windows and doors.”
At that moment, I realized this wasn’t about windows at all. It was a test — not of my general knowledge or trivia skills — but of how I handle ambiguity, how I think, and how I break down problems with missing data.
So, I took a deep breath and started doing what I do best: breaking it down.
Here's how I approached it:
Assumption 1: Berlin has about 4 million residents.
Assumption 2: Let’s say 3 people on average live in one apartment — that gives ~1.33 million residential units.
Assumption 3: Each apartment might have around 6 windows. That’s ~8 million residential windows.
But that’s just the beginning.
Non-residential buildings: Offices, schools, government buildings, fire stations, train stations — these might account for 30-40% of the total built area.
Assumption 4: Let's assume 40% of total windows are in non-residential buildings. So that’s another ~5.3 million windows (40% of the total so far, 8M / 0.6 * 0.4).
Then there’s more:
Car windows? Berlin has over 1 million registered vehicles. Assuming 6 windows per car on average, that's another 6 million windows.
Buses, trains, trams: Public transport counts too. Let’s roughly add another 2 million.
By then, I was sketching all of this out with pen and paper — no Mac calculator, no fancy tools. The interviewer smiled and said, "There’s no right answer."
I landed on around 24 million windows. Could be off by a lot — and that’s okay.
Why do interviewers ask questions like this?
They’re not testing if you know the number of windows in Berlin. They’re testing:
Can you stay calm under uncertainty?
Can you estimate based on assumptions?
Can you explain your thought process clearly?
Do you get flustered or do you start building a solution, even with limited info?
This type of question is common in product roles, data, consulting, and tech interviews — where problem-solving is core to the job.
How to structure your answer to questions like this:
Clarify the problem: Ask what kind of "windows" we’re talking about.
Make clear, reasonable assumptions:
* Population
* Household size
* Window count per unit
* Non-residential ratio
* Cars and public transport
* Other structures (warehouses, greenhouses, etc.)
Break it into categories: Residential, commercial, transport, public buildings.
Estimate with numbers: Don’t aim for perfect. Just reason it out.
Summarize your result and acknowledge the margin of error.
Final thoughts:
If you ever face a question like this in an interview, don’t panic.
Remember:
It’s not about being right. It’s about how you think.
Stay calm. Start with assumptions. Break it down.
Be transparent in your logic and walk them through your reasoning.
Don’t rush. It’s okay to take a minute to think or even sketch.
The real test is: Can you make sense out of chaos?
This was one of the most fun and challenging moments I’ve had in an interview — not because I knew the answer, but because I had the chance to show how I solve problems when there’s no clear path forward.
What’s the most unexpected interview question you’ve been asked?
Top comments (2)
Very nice, thansk for sharing the story.
try this if you get stuck during the interview. its an AI co-pilot that solves the questions for you so you can focus on the more important part of the interview, the communication part. its also a really good study tool: ghostengineer.com