I had an interview at a major tech company with a similar thing, for a more managerial role.

The question was to estimate how many vacuum cleaners there were in the city we were in.

Fine, I did some estimation of how many vacuum cleaners per household and per office, across how many households and offices. Standard stuff.

Then the guy starts laughing and saying I'd failed because I didn't include discarded vacuum cleaners in landfills. Or the vacuum suction devices they put in your mouth at the dentist's office. And so forth. And then had to spend the next five minutes listening to him "teach me" how not to make assumptions. So I acted all polite and tried to fake "oh gosh thank you so much for enlightening me!"

Shockingly, I got the job, which required unanimous approval from all interviewers. Never met him again, and to this day I still have no idea whether this was supposed to be a test of estimation (which was easy to pass), a test of not making assumptions (which is dumb, but OK fine I failed), or a test of being appropriately professional and smiling in the face of complete bullshit (which I'd say I passed with flying colors).

I mean, in my professional life I've certainly had my fair share of customers and managers and coworkers who spout bullshit and you really do just have to lie with a smile and say "oh my gosh you're so right thank you for explaining that, I appreciate you so much!" Where you need to make them feel smart.

On the other hand, I just don't think he was thinking that far ahead.

Is the landfill actually 'in' the city, or in a rural area outside the city limits?

I had a similar interview years ago - something like "how many windows are there on houses in our town?". Wasn't quite that, but I asked up front if "houses" meant just physical standalone houses, or if they meant living spaces, including apartments/dorms, etc. I got clarification, gave some estimate with some reasoning, and was then told I was the only person of the 8 they'd interviewed that had asked any clarifying question at all, which apparently impressed them enough to make an offer.

Yes, I have used questions like this before for junior roles and the notes for the interview were something like:

- Asked/did not ask clarifying questions

- Did/did not (or could not, on prompting) verbally walk through their reasoning

- Could/could not articulate which assumptions they felt were most important/why

Nothing about the actual content of the question itself, or if your answer was approximately correct (I usually did not know even the ballpark of the correct answer myself). I will say I did sometimes write down if candidates make comically bad assumptions. Like assuming the population of the USA was 1 Billion people. It's a fine line on what is "comically bad" but like, if you are interviewing for a startup of 20 people and you use $20B/year as the revenue assumption with no wink. That's a red flag. Lmao.

Yeah, I think there's a possible pitfall with using this as an interview technique though.

When you're in a real situation with a customer or user, you ask tons of questions. You use a lot of common sense to figure out what they really want, what's actually important, etc.

But often times these interview questions -- like how many vacuum cleaners in a city -- don't need any further questions asked. The idea that you'd count vacuum cleaners in landfills, or dental suction devices, is just silly. In real life, if someone wanted to know about the vacuum cleaners in landfills too, they'd tell you in the first place.

If an interviewer wants to see if someone can ask clarifying questions, they'd better come up with a scenario where it would make sense to ask them in a normal conversation. Scenarios that are genuinely ambiguous to anyone with common sense.

Otherwise interviews become this weird cargo-cult thing where you have to learn that interviewers present common-sense clear questions, but you have to ask silly clarification questions that you wouldn't in real life, just so somebody can check a box that you asked questions.

Yeah I mean the vacuum landfill thing is stupid. The point was never to try to trip people up, there's no wrong answer (or question), just find out if they could recognize ambuiguity. "Let's try to estimate the amount of pet food sold each year in the USA." -> "Dogs and cats too?", "In terms of dollars or pounds of food?" type of stuff. This was for analyst roles - basically your whole job would be something similar to this where you're asked ambiguous questions and you need to translate that into a semi-rigorous analysis, infer intent, etc. I hate to say it but if you didn't realize that going into the interview, you were probably not a good fit as an analyst in the first place!

Well cannot agree really.

Assumption is mother of all fuckups.

I’ve seen customers wanting X and assuming that you should know that X comes with A and B because everyone in their business knows that. But you implement only X with A because you made your own assumptions and did not ask. So you missed the deadline and customer that’s it.

> Like assuming the population of the USA was 1 Billion people.

Is that comically bad? It's only like three times too much (if you're using the American, 10^9 billion), but we'd accept a much greater margin of error in some other assumptions (like in the classic 'how many Piano tuners are in the city', I think an assumption of 1-in-30 or 1-in-300 households having a piano (that would need tuning) all sound like they could be true!)

Totally my personal opinion, but not knowing the approximate population of the country you live in betrays a pretty serious lack of curiosity about the world. Obviously a judgement call on how far off is "far off", but it just gives a funny feeling, you know?

True, but in the context of making a ‘finger in the air’ calculation, 1 billion or 100 million (approximating to the nearest power of ten) should be “good enough’.

And if you’re interviewing, consider that for a decent proportion of people it may not be the country they live in (at least at the time you’re asking the question).

Great interview from a certain perspective. You knew for sure (if you had a choice) that you didn't want to work for this specific person.

> How on earth does that indicate if a junior frontend dev can do their job or not?

Playing devil's advocate, maybe a junior frontend dev that doesn't trust that they understand what someone is asking for and pushes back on bits that should be obvious will perform better (in some contexts?) than one that doesn't.

For a junior role in particular, though, it really doesn't seem like that should be the threshold and it sounds like it was delivered poorly on top of that.

Might be good as an exercise in a workshop on requirements gathering, as part of an interview absolutely stupid.

I hear what you’re saying, but really, this is a stupid question and a waste of everyone’s time. Instead you could give a real big report that has insufficient information or that contains a red herring to an improper assumption. The interviewer could then measure if the candidate properly pushed back, exposed an improper assumption and asked relevant clarifying questions. Like one would do at the actual job exhibiting the characteristics the question purports to measure.

The car example is just stupid. Could you image how idiotic you’d sound beginning by asking is it a real car? You’re basically accusing your interlocutor of operating in bad faith (which they were).

> really, this is a stupid question and a waste of everyone’s time

Yeah, I think I agree. I was just responding to (what I saw as) sentiment that it was entirely unrelated to performance, which seems to overstate the case.

> Could you image how idiotic you’d sound beginning by asking is it a real car?

Tbh, "willing to sound like an idiot to double check assumptions" is probably something worth selecting for! I don't think that saves this question, though.

Not just that, but the person said they did ask the interviewer what kind of car it was and what it was used for, at which point any reasonable person would explain it was a toy!

That interview question is basically, "We lied about an imaginary situation and were disappointed you failed to accuse us of lying mid-job interview."

That just feels like playing chess with a pigeon