5 ms·

I interviewed at Google (back in 2005, mind you) and I remember being asked a couple brain teaser questions like how to estimate the number of windows in NYC.

I interviewed at Google (back in 2005, mind you) and I remember being asked a couple brain teaser questions like how to estimate the number of windows in NYC. I will say that out of my loop, there were only 2 interviewers that came across as intentionally mean, the rest were genuinely wanting to see how I solved problems and understand what my thought process was, which is what most interviewers should be attempting to assess. The intentionally mean ones need to be culled from your interviewer pool though. Does it really do a service to Google or to the candidate to stump them, and also humiliate them for not knowing the answer you were hoping to get from them? There are ways to make a candidate feel good about failing an interview despite not making the hiring bar. And remember, these candidates are still your customers, and human beings. They will remember how they were treated.

mgraczyk 8y ago
This was 13 years ago, and Google has since had many "revelations" about its misuse of useless tools like brainteasers. The current process and interviewer training/selection process is nothing like the process in 2005.
- jlarocco 8y ago
  Perhaps that true, but I think it's a recent change. I vaguely remember having a brain teaser question as recently as 6 years ago, but I concede it was a long time ago and I could be remembering wrong. BI had an article about it as recently as 2015. https://www.businessinsider.com/google-brain-teaser-interview-questions-dont-work-2015-10/ https://www.businessinsider.com/google-brain-teaser-intervie...
  - groby_b 8y ago
    BI... is an interesting publication. With an interesting relationship to facts.
pzh 8y ago
Aren't the examples of brainteasers actually Fermi problems? Maybe they sound like brainteasers if asked without the appropriate context, but when you're doing a system design interview and you have to estimate your throughput or storage requirements, you're effectively solving a Fermi problem just like the one that asks you to estimate the number of windows in NYC.
- gamegoblin 8y ago
  Most of the "estimate foo" problems are Fermi problems. E.g. The classic one I've heard is "estimate the number of piano tuners in the world". The route I took to do so is: number of people in the world / average number people per piano * average number of times a piano is tuned per year * average amount of hours to tune a piano / average number of hours a piano tuner works per day / average number of days a piano tuner works per year So in terms of units, the flow is: people -> pianos -> piano tunings per year -> hours spent tuning pianos per year -> workdays spent tuning pianos per year -> piano tuners This is all very similar to dimensional analysis most people will learn in a highschool science class. Just to plug in some random numbers, let's pick 7 billion people, 100 people per piano, 0.3 tunings per year, 1 hour to tune a piano, 3 hours of tuning per day and 100 days per year(I imagine it's part-time for most piano tuners...). We arrive at: 7,000,000,000 / 100 * 0.3 * 1 / 3 / 100 == 70,000 And, for what it's worth, at least in my field, we do these sorts of ballpark estimations all the time to determine feasibility of systems. I've never had one of these in an interview setting, but I imagine the important thing is to demonstrate the line of reasoning rather than actually arriving at a concrete number.
- dogecoinbase 8y ago
  I love the term "Fermi problem", because the origin is, of course, the Fermi paradox. The idea that multiplying a series of uncertainties together does something other than blow your error range out is such a weird idea.
  - rumcajz 8y ago
    Related: https://arxiv.org/abs/1806.02404 https://arxiv.org/abs/1806.02404
smelendez 8y ago
That question doesn't seem great. People who've spent more time in NYC will likely perform better, since they'll immediately start describing classes of buildings where they've spent time and generalizing, but how familiar you are with NYC is irrelevant to the job. Depending on your applicant pool, that might be correlated with a protected class, like race, gender, or national origin.
- ummonk 8y ago
  I don't think classes of buildings are that imporant. Just multiply the resident population by the number of windows per person. Just throwing a number out there, I'd estimate something like 10 windows per resident, counting residential and commercial.

mgraczyk 8y ago

This was 13 years ago, and Google has since had many "revelations" about its misuse of useless tools like brainteasers. The current process and interviewer training/selection process is nothing like the process in 2005.

jlarocco 8y ago
Perhaps that true, but I think it's a recent change. I vaguely remember having a brain teaser question as recently as 6 years ago, but I concede it was a long time ago and I could be remembering wrong. BI had an article about it as recently as 2015. https://www.businessinsider.com/google-brain-teaser-interview-questions-dont-work-2015-10/ https://www.businessinsider.com/google-brain-teaser-intervie...
- groby_b 8y ago
  BI... is an interesting publication. With an interesting relationship to facts.

pzh 8y ago

Aren't the examples of brainteasers actually Fermi problems? Maybe they sound like brainteasers if asked without the appropriate context, but when you're doing a system design interview and you have to estimate your throughput or storage requirements, you're effectively solving a Fermi problem just like the one that asks you to estimate the number of windows in NYC.

gamegoblin 8y ago
Most of the "estimate foo" problems are Fermi problems. E.g. The classic one I've heard is "estimate the number of piano tuners in the world". The route I took to do so is: number of people in the world / average number people per piano * average number of times a piano is tuned per year * average amount of hours to tune a piano / average number of hours a piano tuner works per day / average number of days a piano tuner works per year So in terms of units, the flow is: people -> pianos -> piano tunings per year -> hours spent tuning pianos per year -> workdays spent tuning pianos per year -> piano tuners This is all very similar to dimensional analysis most people will learn in a highschool science class. Just to plug in some random numbers, let's pick 7 billion people, 100 people per piano, 0.3 tunings per year, 1 hour to tune a piano, 3 hours of tuning per day and 100 days per year(I imagine it's part-time for most piano tuners...). We arrive at: 7,000,000,000 / 100 * 0.3 * 1 / 3 / 100 == 70,000 And, for what it's worth, at least in my field, we do these sorts of ballpark estimations all the time to determine feasibility of systems. I've never had one of these in an interview setting, but I imagine the important thing is to demonstrate the line of reasoning rather than actually arriving at a concrete number.
dogecoinbase 8y ago
I love the term "Fermi problem", because the origin is, of course, the Fermi paradox. The idea that multiplying a series of uncertainties together does something other than blow your error range out is such a weird idea.
- rumcajz 8y ago
  Related: https://arxiv.org/abs/1806.02404 https://arxiv.org/abs/1806.02404

smelendez 8y ago

That question doesn't seem great. People who've spent more time in NYC will likely perform better, since they'll immediately start describing classes of buildings where they've spent time and generalizing, but how familiar you are with NYC is irrelevant to the job. Depending on your applicant pool, that might be correlated with a protected class, like race, gender, or national origin.

ummonk 8y ago
I don't think classes of buildings are that imporant. Just multiply the resident population by the number of windows per person. Just throwing a number out there, I'd estimate something like 10 windows per resident, counting residential and commercial.