How many people using facebook in San Francisco at 2:30pm on a Friday?

About 60 percent of adults (18+) Americans have a Facebook account. But we're talking San Francisco here--the Valhalla of Nerdery and all things internet--so lets bump that up to 80 percent (this 30 percent increase is justified by the fact that SF is 30 percent geekier than anywhere else...). For purposes of the question, let's limit this explicitly to the city of San Francisco--not the entire Bay Area. At night, SF is about 800,000 people strong. Let's assume a little over 20 percent of that population is either too old or young to use Facebook (it would be higher if mothers hadn't taken off FB...). Let's say that leaves 600,000 people (note: working with round numbers is better for these sorts of things). But then we have to take into account the fact people commute to and from SF! Nerds pour out into the South Bay, suits (e.g., bankers) come in from the East. I suspect the city population swells by 50 percent. If we toss in tourists and conference goers and everything else, 1 million people are in San Francisco at 2:30pm on a Friday. Eighty percent of those people use Facebook, so we have 800,000 possible Facebook users at that time. The final step is to figure out what percent of the 800,000 are using Facebook at 2:30pm. It's later in the day so I suspect it will be higher than at 11:00am. But I don't really have a good baseline to judge. When I walk around my office, roughly 10 to 20 percent of screens I see as around the office are on some non-work related thing at any time. Let's call that 15 percent and assume that all non-work related surfing by FB users includes some sort of use of FB. That means 120,000 people are using FB at 2:30pm on Friday in San Francisco.

Answer?... more than are using Google+

All of them. Facebook's corporate HQ is in Menlo Park, a suburb of San Francisco. So, anyone using Facebook is using "Facebook in San Francisco".

I think that there can only be one motive behind asking such a stupendous question, i.e., to see your thought process, and to see your assumptions behind your guesses, how deeply did you think about the problem, how many dimensions did you look at, before formulating a 'plan'? Such questions are best tackled by doing a quick internal-brainstorm session while thinking aloud~so that your interviewer also gets a glimpse of your inner-mind's working. In this respect, i think that GBAD has done a good job of making his/her assumptions clearer than the rest of us.

I compare these oddball questions to the Men in Black Scene where J is trying out against the "best of the best"......these companies are trying to find the out of the box thinkers. Many seem to use their education, assumptions, statistics, logic, and deduction to come up with the answers. Answering the question is the first mistake most interviewee's are making. I think these big companies would probably hire Tim first over GBAD. Why Tims? There's no way Google could argue nor find flaw in that statement. They know where Google+ stands, and they can't disprove that as false. Whereas GBAD, they'll probably start questioning him on where he came up with the stats. It's not about the right answers, it's about how they can prove you wrong. So don't let them prove you wrong.

God, Is that really strong logic? Where did you get the 10%? I would think that at 2:30 on a Friday more than 10% of the working population have Friday-itis and are surfing facebook to plan their weekend

A; Who cares I'm not one of them! I'm still at work!

Let me google that for you. If the answer isn't readily available, I'll E-mail someone at facebook analytics. No one will surmise a closer answer.

All of them. Meaning people. Who else would be accessing Facebook in the first place, a dog, cat, squirrel? It's like the question asked when passing a cemetery...How many people are buried there?...Silly fools. All of them. LOL.

To Barney, the population of SF is only about 800,000.

The answer is-- The number of people on Facebook in SF minus the number of people not using Facebook at 2:30 that Friday

there is no right or wrong way to approach the answer to this question. There is also no right or wrong answer. They only want to see what logic you are using to come up with the number. It is a similar question that I believ Microsoft, it could be Google though, asks when asking how much would you charge to wash all the windows in Seattle. you can multiple and divide and subtract and add the population by the work force, avg height of the building, and come up with a number, or yo can simly say 10 bucks a window.

Too many.

@AL: you're right to point out that these questions can be used to assess creativity. but more often than not, when asked by a big company like google or any of the consultancies, they want an answer. they want to see how you make assumptions--even if the final number if way off. if you can sprinkle in some creative bits, that helps. but you typically need a number at the end.

Me: None Interviewer: How could you ever know that? Me: San Francisco is far too techsavy to use such an outdated technology, they're on google+

GBAD's approach is correct. This type of interview question is referred to as a brain teaser. Most of the large management consulting firms throw these types of questions at you, along with business cases that require you to compute numbers and rationalize your way to a solution. The interviewer is not interested in the answer you come up with here. He is interested in the thought process and your analytical problem-solving skills used to find an answer. A similar question used is: "How many ping pong balls would fit in the body of a Boeing 777?" Yet another: "How many boxes of Count Chocula cereal were sold in the United States last year?" They don't want you to respond by saying you'd look at the sales figures from General Mills. They want you to come up with something on your own. They want to see your methodology. These types of questions separate the best from the best. If you'd like more information on these types of interviews, Google "McKinsey consulting interview questions."

ANS: I don't know. May be if facebook uses google analytics, then that can help!

I would ask in return, Can you tell me a little bit about how the answer will be utiliized . Data is data but depending upon how it will be used, depends on the answer. Turn it around for just long enough to allow the interviewer a chance to show off while you come up with a valid answer. And because you will not have your computer available use the above advice and give a generic answer about how you would progress to acquire this information. Certainly they most probably do not care what the technical answer is, they want to knowcan you process problems and create solutions.

Correction: GBAD has provided the best analysis.

@God, Daniel answered the question in a clever way, but somehow you missed it, despite your all-seeing nature. He simply read the question with a different emphasis: How many people using *facebook in San Francisco* at 2:30pm on a Friday? rather than *How many people using facebook* in San Francisco at 2:30pm on a Friday?

I would have been inclined to ask a "qualifying question" - What problem are you trying to solve? If as I suspect Tim's presumption is correct, perhaps the interviewer would have admitted it and then you could offer your expertise in correcting that condition.

Simply put many people. Are we talking about people that live in SF as well as people born there that live elsewhere? Is this including people on planes travelling elsewhere on facebook? For how long does the user have to be on facebook to be included? 2 guards......one holds the door to life and freedom, the other death. You can ask one question to one guard. What question do you ask?

Plus or Minus 10% that were using it at 2:29:59. Except on the Friday with the earthquake. If the interviewer asks which was that Friday then you tell him :"Please you answer that because I want to see the caliber of the people that I will work with assuming I will accept your offer."

given its a friday and its already 2:30 pm.... ill say more people are using facebook than any other weekday as they will be planning the weekend with their friends.

This is a question asked by Google. Clearly, they want you to Google the answer.

Its questions like these force me to be self-employed. I have a low tolerance for mind games. I would answer this question with a statement. I don't know the answer. Can you tell me why this information is important to you and how it pertains to the position I am interviewing for? The I would wait for their answer, and respond to that. .

Comparatively less than the people using google @ d same time (keeping in mind that the question was asked by google for the post of VENDOR RELATIONS MANAGER).

Isn't the interview question incomplete or grammatically incorrect?

None. They all should be using Google+

1159 less than the people active on Whatsapp in San Francisco at 14:31 on a Wednesday.

Well, Siri didn't know.

Seems like a Fermi question isn't it? http://en.wikipedia.org/wiki/Fermi_problem

The answer should revolve around the actual position your are applying for. For instance, TNT's response to qualify the question would be a great answer for a sales position. GBAD a statistician or someone involved in marketing research. Always answer a question in which is applicable to the job. THERE IS NO CORRECT ANSWER. However I did think whoever said "everyone, because facebooks headquarters is in San Francisco" is a clever enough answer for any position. I will also say that ultimately the idea is to see how you handle the question, which is applicable in any position. If you don't answer with confidence, no matter what you think, I wouldn't be excited to hire you.

Florin - Remember that people hire people that they feel reinforce their values and sensibilities. In the consulting field they call this mirroring - you mirror the values, etc., of the client. Mirroring works great for client engagements. They may be assessing your fit with the company with a the "brain teaser" but I find it unlikely that all they are interested in is you cold analytical abilities in figuring out an absurd question. Analysis may be part of the puzzle but it will also be in how you respond to them as people, how you make your argumment - in short - are you one of them and will you fit? The moral to this whole story will be simple and is something you've known all along (your mom and dad probably told you this) , be yourself. If you don't fit, the job will not work out for you in the long run anyway for a lot or reasons including because you won't be happy there because, well, you don't fit. So be yourself and be CONFIDENT in who you are. If the fit is there you've hit a homerun. If not, it's just a job.

All of them. Melissa is right, oldest most logical answer out there.

equal to the no. of gmail users....

This is where you show off your technique rather than your memorized set of facts. The interviewer is interested in your powers of deduction as well as your prowess in planning an estimate. First of all, it is necessary to define the term "using". Possible definitions include: have an active session with; exchanging data with; displaying the website in some viewer; etc. Someone having the right kind of network access, assuming you could contact her, would be able to count the number of active sessions, but this would return a count of endpoints rather than of "people". Further refinement necessary. Given the number of variables and the uncertainty in each, the crucial part of the answer will be to pin down a confidence interval.

After reading though the list of questions and answers I offered the following observation on the Tesla question and am repeating it here on the first question: These questions (all 25) on the most part seem to be using the psychological projective test technique. In projective tests the questions are designed to be ambiguous. It's like looking at an inkblot and telling me what you see. Because it's random with no clear answer, you have no choice but to “project” your personality, thoughts and feelings in the answer. Thus revealing something about yourself that the interviewer may find useful and hopefully job related. For example, those of you who obsess over the technical details or those of you who offer a glib response or those of you who ask why is the question relevant. These answers all attest to an aspect of your personality. That said, while I like the idea of projective tests I suspect that these questions are mostly amateurish attempts at projective tests that have not been validated or shown to be job related- I would be surprised (if not heartened) if otherwise.

Thanks GBAD and MM. I am actually preparing myself for a consulting position and have done tons of preparations. That is the way such a question should be approached. As MM mentioned the interviewer is "interested in the thought process and your analytical problem-solving skills''. It is not a tricky question, and at the end, they want a NUMBER. MM has provided the most in depth analysis. Paul's answer is amazing....as an ice-breaker, than...comes GBAD's.

Will go with Melissa on this as most people are offering answers to the question "How many people are using facebook" instead of "How many people using facebook".

At that point I would ask if anybody with half a brain would like to talk to me or should I just leave?

what's facebook ? ;)

Let's Ask Jeeves.

Aditya is correct, although fascinating how many ppl show their lack of problem solving, including GBAD. Extra bonus points for Tim's answer, because he probably answered the question that created the question in real life. "The final step is to figure out what percent of the 800,000 are using Facebook at 2:30pm" Actually no, you already said that was the night population of SF, so therefore you're basis is way off. Many more people work in SF during the day than live at night, so toss the 800k figure out to start. And Daniel Gullo, decent answer, but the question didn't ask what percentage of users were in SF. That's what you answered. So... let's see. I'd guess there to be around 1.5m people in SF on a random Friday @ 2:30, maybe 10% of which are actually on FB. Easy as pie answer of 150,000. Correct or not, the logic is strong, and that's the point.

"How many people on facebook...." 4, 573, 210. Prove me wrong.

This is good feedback, but i'd also be curious to know why Facebook and not Google +?