The Trickiest Interview Question I Never Saw Coming

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:

1. Clarify the problem: Ask what kind of "windows" we’re talking about.

2. Make clear, reasonable assumptions:

*   Population

*   Household size

*   Window count per unit

*   Non-residential ratio

*   Cars and public transport

*   Other structures (warehouses, greenhouses, etc.)

1. Break it into categories: Residential, commercial, transport, public buildings.

2. Estimate with numbers: Don’t aim for perfect. Just reason it out.

3. 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?