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Comment by tommiegannert | Hacker News Reader

I interviewed for a company in London ten years ago (being from Sweden and flew in the day before.)

Interviewer: "How much water flows through the Thames?"

Me: "Well, I sat next to the Thames once, and it's maybe 50 m across. Depth... I dunno 10 meters? Speed..."

Interviewer: "Actually... It's 100 m across and..."

I could see the interviewer realizing this wasn't the most relevant question to ask to someone not from the area. Perhaps they wanted that interaction, I don't know. A silly question that just dealt with local knowledge, and (in the end) very little modeling.

I played along, then sat in my hotel room and shook my head.

However, one of my hard rules is that I don't spend more time on the hiring process than the company does. I'll happily sit and talk to an employee for four hours, but I'm not going to do a "take-home test" for more than 10 min.

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Actually 100m across where? At London Bridge it's 265m wide. At the mouth it's 18 miles across. At the narrowest point it's only 18m across. At Oxford it's 46m, so you could say you only know the Thames from your time at Oxford.

What a stupid thing to ask in an interview. Answering that would prove... what? That you can multiply and make some wild guesses about a geographic detail you aren't familiar with?

I interviewed for a job in Sweden a long time ago (I'm a US citizen). The hiring team took me to dinner, and I got the impression my future at the company (or not) depended on my willingness to eat every kind of fermented fish offered at the restaurant. They didn't ask me how many liters of water Lake Mälaren holds.

Actually, not just where, but in which direction? Because during high tides the water can flow backwards up to the Thames Barrier in Greenwich, which they can close if it is too much.

And if you are from Sweden you can ask back: how many IT people does it take to eat a single can of surströmming? It is at least as relevant to doing the job well and to mix with locals, isn't it?

I'm thinking about the Bridge of Death scene in Monty Python and the Holy Grail.

"Where on the Thames do I measure the flow? And what time of day and day of the lunar month?

"What? I don't know that!" Then the interviewer plunges into the gorge of eternal peril.

> Answering that would prove... what? That you can multiply and make some wild guesses about a geographic detail you aren't familiar with?

Yeah, it was just weird. The interviews by the team in California were better, to be fair. (Though I still don't understand why they had to fly me there. The day after a 15 h flight across timezones, they spent 8 h giving me brain teaser questions. I was toast after that.)

> my willingness to eat every kind of fermented fish

That would have been my cup of tea!

I once got asked how many first-grade pupils is there in a country I'm not from. I challenged the question and said that I have no way to know that since I'm not from the country and I doubt it's relevant to the position I'm being interviewed for. When pushed to answer I said "about 1% of population", the interviewer was not satisfied with my answer because I refused to elaborate why 1% and not more or less. On my way out I googled the fact to find out it in fact is 1% of the country's population.

The point of the question isn’t trivia or mathematics, it’s to demonstrate how you deal with ambiguity

At work you may be asked to spec out and implement a poorly-defined defined request.

They expected you to have asked clarifying questions rather than steaming ahead in the assumption that the Thames is 50m metres wide at all point.

The interviewer stating “actually it’s 100m” shows that they didn’t understand this point either though, and was probably repeating the answer they were told to give if the candidate asks this clarifying question

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