> Edit: More perls; "What is the angle at 3:15?" humm 0?
This question is about how angles are measured on a clock face, there are 2 methods where you either use hours (360/12) per hour, or minutes (360/60) per minute.
So at 3:15 the angle will be 30x3+30/4 or 97.5 degrees from 0 or just 30/4 which is 7.5 if the hour is your starting point.
> Edit: More perls; "What is the angle at 3:15?" humm 0?
It's not 0. At 3:00 sharp the angle is 90 degrees. 15 Minutes later the minute hand covered those 90 degrees, however the hour hand moved by a small amount too.
Wrong answer to both questions. 0.0025 % of 60,000 numbers is 1.5. I can name more numbers without a 6 than that; 1 and 2, for example. Other commenters already wrote about the angle.
If I asked that question in a job interview, I'd expect the following mistakes:
0. Missing high-school-level math skills.
1. Double-counting numbers with double sixes (e.g. counting 666 three times)
2. Either failing to count the number 60,000 or mistakenly counting numbers 60,000-69,999
3. Failing to invert the result (i.e. counting the probability it /does/ have a six, instead of the probability it /doesn't/ )
4. Getting a result that was off by several orders of magnitude, and not noticing it.
5. Messing up the mental arithmetic (this is the reason I wouldn't use this question in an interview)
In other words it's a test of diligence and being able to get the right answer to simple problems. Which is a valuable quality in an industry with so many off-by-one errors!
You're pretty far off man. Assuming we're uniformly sampling the whole space, I thought of it as five independent games of choosing each digit, then "winning" each time by not getting a six. So the probability of 5 wins i.e. A number without a six is (9/10)^4 * (5/6). But that counts from 0 to 69,999. If we count up to one less in the tens of thousands place (5/5) we get 0 to 59,999. Which is off by one in both directions. So we can "slide" the window up but 0 was number without a 6 but 60,000 isn't so we have to discount another choice. Leaving us with (9/10)^4 * (5/5) * (59999/60000) = 0.656089065 or 39365 out of 60000.
The clock question always pissed me off in school. It assumes the clock's arms move in a continuous way. The clocks I grew up with made discrete movements.
The capital of Canada is an unbelievably tough interview question? Is Ottawa that obscure or have we lowered our standards of geographical knowledge to kindergarten level?
One of my favorite capital questions is "Capital of Australia". People invariably end up with Melbourne. They are surprised when it turns out to be Canberra - a city which in all likeliness they have never heard about.
Sorry, I would not have been able to tell you that answer. I have never cared much for geography and I literally never need to know other country's capitals in my day to day life.
It's reasonable for people in the US to know it. I do but then I've been there. But I'm not sure it's that much more basic knowledge than the capital of California, Texas, or New York if you don't live in those states.
Most people think the capital of New York is New York. Ottawa isn't exactly on anyone's world destination list. Completely reasonable that the majority of people wouldn't know that.
A few of these are reasonnable to see how someone is able to explain a concept or make sense of something very anstract. Most of them though would make me walk out the door in a heartbeat.
The water lever would rise (imperceptibly)
The weight of the rock displaced its weight in water while in the boat, when it sinks it only displaces its own volume.
This article is a thinly veiled ad for their own site. Clickbait title, starts off with an implication that to prepare for interviews you should be reading their site... oh, and then sure, they write an article, too. But everyone on HN should be clever enough to see through this as little more than cheap marketing.
The sad thing is that I'm currently job hunting, I'm interested enough to give a minute or two of my day to review some content of this type, I do use their website to review companies, but then... they have to go and cheapen the whole experience for both of us by coming on so hard.
Now, instead of being mildly intrigued by what they had to offer, I just feel dirty for looking and want to go take a shower.
Exactly, resolving ambiguity is the main thing I look for in interviews. It's actually a very important skill. Business requirements are often ambiguous and I need someone who can ask questions to make the more clear.
It seems like it would take about a minute to work it out.
1x25c
2x10c
3x1c
It's pretty nearly the first thing you'd probably try.
(2 quarters can't work, so it must be 1 or zero, let's assume one, 23 cents left, 3 dimes can't work, let's assume 2, 3 cents left, no nickels can work, 3 pennies, done)
And nowadays we have google for some added prosthetic knowledge. It's becoming increasingly important to grasp concepts well enough to ask the right questions, but knowing simple unrelated facts by heart becomes irrelevant. At most you have to remember that there was something to remember so you can look it up.
edit: can a native speaker guide me on where to set commas correctly :) ?
"A hundred prisoners are each locked in a room with three pirates, one of whom will walk the plank in the morning. Each prisoner has 10 bottles of wine, one of which has been poisoned; and each pirate has 12 coins, one of which is counterfeit and weighs either more or less than a genuine coin. In the room is a single switch, which the prisoner may either leave as it is, or flip. Before being led into the rooms, the prisoners are all made to wear either a red hat or a blue hat; they can see all the other prisoners' hats, but not their own. Meanwhile, a six-digit prime number of monkeys multiply until their digits reverse, then all have to get across a river using a canoe that can hold at most two monkeys at a time. But half the monkeys always lie and the other half always tell the truth. Given that the Nth prisoner knows that one of the monkeys doesn't know that a pirate doesn't know the product of two numbers between 1 and 100 without knowing that the N+1th prisoner has flipped the switch in his room or not after having determined which bottle of wine was poisoned and what color his hat is, what is the solution to this puzzle?"
> 4. “Who in history would you want to go to dinner with and why?”—Flight Attendant, PSA Airlines
I was asked a similar question, but in a quite different context. I was on jury duty in the Los Angeles area in July, 1987. Our panel was sent to a courtroom that needed a jury for some drug charge. The procedure was that 14 from the panel would sit in the jury box (12 jurors plus 2 alternates), where we'd be questioned by the judge and lawyers, and if any of us were rejected for that jury, someone else from the panel would take their place and be question. Repeat until there are 12 acceptable jurors.
One of the questions the defense attorney asked us was if we could have dinner that night with anyone in the world, living or past, who would we choose? I was in the fifth seat in the front row, so had some time to think before he got to me. The answers ahead of me were the candidate's deceased mother, Richard Feynman, Pope John Paul II [1], and I forget the other.
Then he asked me.
I said "Adolph Hitler".
A lot of the panel that was not in the box (maybe 30 people) had been kind of nodding off, as this was boring, and the courtroom was hot (it was the middle of summer, and the courtroom was not air conditioned). My answer woke them all up.
The attorney asked why and I explained that Hitler did terrible things to other people, and was clearly insane. That makes him at least interesting, but not unique. What sets Hitler apart, and makes him a good candidate for dinner, is that he somehow got a lot of apparently sane, rational, educated, well-off people to willingly help him commit his atrocities. He must have had tremendous charisma or something in order to get those results, and so a dinner with him should be very interesting.
The prosecutor also asked us a far out question. She asked us what we would say if aliens (the space kind, not the human from another country kind...) contacted us and said they had been monitoring our news and were confused about the "drug problem", and asked us to explain it.
I told her that I would tell them that we have arbitrarily classified some drugs as illegal and some as legal, without much regard to the actual harm of each, and so we have some drugs legal (alcohol, tobacco...yes, I know these might not scientifically be drugs, but for purposes of drug law policy they are effectively drugs), and some illegal (marijuana, LSD, cocaine, heroin, for instance), even though some of the latter group (such as marijuana) do the same or less harm than some in the former group. Then on top of that we don't admit that this is arbitrary and irrational, and so our schools, police, and government lie to kids telling them that drugs like marijuana are as bad as heroin. Of course, the kids end up trying marijuana, find out that they were lied to, and then do not trust the advice they've received on other drugs, and so likely end up trying drugs that really ARE bad. And then we waste a lot of money trying to enforce these stupid laws on things like marijuana when we could be putting that money and time toward real problems. She tried to defend the drug laws and policy, and we argued for a bit before she moved on.
So...basically...I told the prosecutor that this case was stupid and irrational, and she is working for a system that purposefully lies and makes the problems worse. Oh, and I had long hair and a beard and was wearing a tie-dye shirt that made me look like a hippy who had just come from a Grateful Dead concert and was probably on drugs right now.
I was pretty sure at this point that I was not going to make it onto that jury. The only question was whether it would be the defense or the prosecution that used one of their three peremptory challenges to kick me off.
I was guessing it would be the prosecutor, because I had basically told her I considered this whole thing stupid and harmful. On the other hand, I did say when asked that I would vote according to what the law says, regardless of how stupid I thought that law or its applicat...
> “Prove that hoop stress is twice the longitudinal stress in a cylindrical pressure vessel.”—Test Operations Engineer, SpaceX
Well, I have no idea whatsoever how to approach that...but I would not be applying to be a test engineer at a rocket company. This sounds like something that an actual rocket engineer should know, and I would guess that it is even something that would be easy for such an engineer.
> “What is the first thing you’d print with a 3D printer if you had one?”—Linux Systems Administrator I, Rackspace
I'd print whatever test object the printer's instructions say to print to verify that I have set the printer up correctly and that it is working.
> “Please describe an instance where you had to make a decision without all of the necessary information.”—Analytics, athenahealth
The obvious answer is "this interview".
> 27. “How would you find the square root of 1.2?” —Hardware Engineer, Jump Trading
I would guess that some context is missing here. I don't think it means that if you needed the square root of 1.2 for something you were doing, how would you obtain it. I expect it is asking how you would do it in hardware, or in firmware. It's then time to talk about what computational ability the hardware has. For example, if it is going to be firmware, is there a divide instruction on the processor? Do we have floating point or are we using fixed point? How accurate does it need to be? Yadda yadda.
If it is asking how you would obtain it for yourself, then the correct answer is use a calculator, unless you just need a quick approximation, in which case it is to note that 11^2 = 121, so 1.1^2 = 1.21, and so 1.1 is a pretty good approximation to sqrt(1.2). If you need slightly better, but still cannot use a calculator, note that 1.1 is slightly high, and assume the right answer is 1.1-x. That gives (1.1-x)^2 = 1.2, which can be rewritten as x = 0.01/(2.2-x). If x is small, we can neglect it in 2.2-x, suggesting we look at x = 0.01/2.2. Let's approximate 2.2 with 2 to make the mental math easier, giving us x = 0.005. That gives us a new approximation for sqrt(1.2) of 1.1 - 0.005 = 1.095. That is quite close. It's square is 1.199025.
If you want an answer that works well under both the "it's for firmware" interpretation and the "it's for me and I don't have a calculator" interpretation is to use the binomial theorem. For square roots, that says sqrt(1+x) = 1 + x/2 - x^2/8 + x^3/16 - 5x^4/128 + ...
With x = 0.2, that's 1 + 0.1 - 0.005 + 0.0005 - ... Note that if you stop at 3 terms you get the same approximation I got earlier, 1.095. Four terms gives 1.0955. That's a good place to stop because 5 terms gets harder to do mentally because of that stupid 5/128.
I believe the hoop stress vs. longitudinal stress question is approximately true specifically for thin-walled pressure vessels. However, it is many many years since I would have been able to prove that--probably about the time I took the final exam in that particular course :-)
Especially given modern computer tools, I'm actually not sure how many mechanical engineers would be able to derive that sort of thing in an interview. I wouldn't have been able to but you probably didn't want me designing rockets either.
53 comments
[ 2.7 ms ] story [ 125 ms ] threadAm I missing something?
9 possibilities (0-9 excluding 6) for each of the last 4 digits and 6 (0-5) for the first one.
6 * 9^4 = 39366
The probability is 100/39366 = 0.0025%
Edit: More perls; "What is the angle at 3:15?" humm 0?
No, not 0, because the hour hand will have moved 1/4 the way to 4, making the angle 7.5 degrees.
This question is about how angles are measured on a clock face, there are 2 methods where you either use hours (360/12) per hour, or minutes (360/60) per minute.
So at 3:15 the angle will be 30x3+30/4 or 97.5 degrees from 0 or just 30/4 which is 7.5 if the hour is your starting point.
It's not 0. At 3:00 sharp the angle is 90 degrees. 15 Minutes later the minute hand covered those 90 degrees, however the hour hand moved by a small amount too.
The probability is 39365/60000
0. Missing high-school-level math skills.
1. Double-counting numbers with double sixes (e.g. counting 666 three times)
2. Either failing to count the number 60,000 or mistakenly counting numbers 60,000-69,999
3. Failing to invert the result (i.e. counting the probability it /does/ have a six, instead of the probability it /doesn't/ )
4. Getting a result that was off by several orders of magnitude, and not noticing it.
5. Messing up the mental arithmetic (this is the reason I wouldn't use this question in an interview)
In other words it's a test of diligence and being able to get the right answer to simple problems. Which is a valuable quality in an industry with so many off-by-one errors!
Brazil is another surprising one.
"The capital of Canada is an interview question?"
What does that show? That you paid attention in geography, that you're Canadian, or that you are able to answer pointless questions?
http://mentalfloss.com/article/30000/thomas-edisons-eccentri...
As you can see, "doesn't prioritize my favorite trivia" was a deal-breaker, even back then.
Some of those questions are perfectly reasonable for the roles. Some are just annoying. It's the gotcha questions that I really can't stand.
> 14. "How do you reverse a text string on the Unix command line?"
Meh... ruby -e "puts 'yourString'.reverse"
It's sort of a weird collection.
Some gotchas as you say. (I wouldn't have been able to do that example off the top of my head.)
A few classic puzzlers like the boulder in the boat. (Which I still needed to think about in spite of having seen it before.)
Some questions of the standard consulting interview type where you have to reason through to a plausible answer about how many of something there are.
Some questions to get you to open up about yourself.
Capital of Canada is just sort of weird. I'd have thought that was easy but wouldn't think less of someone if they answered Toronto.
The sad thing is that I'm currently job hunting, I'm interested enough to give a minute or two of my day to review some content of this type, I do use their website to review companies, but then... they have to go and cheapen the whole experience for both of us by coming on so hard.
Now, instead of being mildly intrigued by what they had to offer, I just feel dirty for looking and want to go take a shower.
But if nobody does it, than Ill do it one day. Now because I wrote it here Ill remember.
That's easy. 2 x 20c and 4 x 2c.
Nobody said the coins had to be American and still in circulation.
It seems like it would take about a minute to work it out.
1x25c 2x10c 3x1c
It's pretty nearly the first thing you'd probably try. (2 quarters can't work, so it must be 1 or zero, let's assume one, 23 cents left, 3 dimes can't work, let's assume 2, 3 cents left, no nickels can work, 3 pennies, done)
And nowadays we have google for some added prosthetic knowledge. It's becoming increasingly important to grasp concepts well enough to ask the right questions, but knowing simple unrelated facts by heart becomes irrelevant. At most you have to remember that there was something to remember so you can look it up.
edit: can a native speaker guide me on where to set commas correctly :) ?
Any answers ???
Ofcourse the answer baffled me
I was asked a similar question, but in a quite different context. I was on jury duty in the Los Angeles area in July, 1987. Our panel was sent to a courtroom that needed a jury for some drug charge. The procedure was that 14 from the panel would sit in the jury box (12 jurors plus 2 alternates), where we'd be questioned by the judge and lawyers, and if any of us were rejected for that jury, someone else from the panel would take their place and be question. Repeat until there are 12 acceptable jurors.
One of the questions the defense attorney asked us was if we could have dinner that night with anyone in the world, living or past, who would we choose? I was in the fifth seat in the front row, so had some time to think before he got to me. The answers ahead of me were the candidate's deceased mother, Richard Feynman, Pope John Paul II [1], and I forget the other.
Then he asked me.
I said "Adolph Hitler".
A lot of the panel that was not in the box (maybe 30 people) had been kind of nodding off, as this was boring, and the courtroom was hot (it was the middle of summer, and the courtroom was not air conditioned). My answer woke them all up.
The attorney asked why and I explained that Hitler did terrible things to other people, and was clearly insane. That makes him at least interesting, but not unique. What sets Hitler apart, and makes him a good candidate for dinner, is that he somehow got a lot of apparently sane, rational, educated, well-off people to willingly help him commit his atrocities. He must have had tremendous charisma or something in order to get those results, and so a dinner with him should be very interesting.
The prosecutor also asked us a far out question. She asked us what we would say if aliens (the space kind, not the human from another country kind...) contacted us and said they had been monitoring our news and were confused about the "drug problem", and asked us to explain it.
I told her that I would tell them that we have arbitrarily classified some drugs as illegal and some as legal, without much regard to the actual harm of each, and so we have some drugs legal (alcohol, tobacco...yes, I know these might not scientifically be drugs, but for purposes of drug law policy they are effectively drugs), and some illegal (marijuana, LSD, cocaine, heroin, for instance), even though some of the latter group (such as marijuana) do the same or less harm than some in the former group. Then on top of that we don't admit that this is arbitrary and irrational, and so our schools, police, and government lie to kids telling them that drugs like marijuana are as bad as heroin. Of course, the kids end up trying marijuana, find out that they were lied to, and then do not trust the advice they've received on other drugs, and so likely end up trying drugs that really ARE bad. And then we waste a lot of money trying to enforce these stupid laws on things like marijuana when we could be putting that money and time toward real problems. She tried to defend the drug laws and policy, and we argued for a bit before she moved on.
So...basically...I told the prosecutor that this case was stupid and irrational, and she is working for a system that purposefully lies and makes the problems worse. Oh, and I had long hair and a beard and was wearing a tie-dye shirt that made me look like a hippy who had just come from a Grateful Dead concert and was probably on drugs right now.
I was pretty sure at this point that I was not going to make it onto that jury. The only question was whether it would be the defense or the prosecution that used one of their three peremptory challenges to kick me off.
I was guessing it would be the prosecutor, because I had basically told her I considered this whole thing stupid and harmful. On the other hand, I did say when asked that I would vote according to what the law says, regardless of how stupid I thought that law or its applicat...
Well, I have no idea whatsoever how to approach that...but I would not be applying to be a test engineer at a rocket company. This sounds like something that an actual rocket engineer should know, and I would guess that it is even something that would be easy for such an engineer.
> “What is the first thing you’d print with a 3D printer if you had one?”—Linux Systems Administrator I, Rackspace
I'd print whatever test object the printer's instructions say to print to verify that I have set the printer up correctly and that it is working.
> “Please describe an instance where you had to make a decision without all of the necessary information.”—Analytics, athenahealth
The obvious answer is "this interview".
> 27. “How would you find the square root of 1.2?” —Hardware Engineer, Jump Trading
I would guess that some context is missing here. I don't think it means that if you needed the square root of 1.2 for something you were doing, how would you obtain it. I expect it is asking how you would do it in hardware, or in firmware. It's then time to talk about what computational ability the hardware has. For example, if it is going to be firmware, is there a divide instruction on the processor? Do we have floating point or are we using fixed point? How accurate does it need to be? Yadda yadda.
If it is asking how you would obtain it for yourself, then the correct answer is use a calculator, unless you just need a quick approximation, in which case it is to note that 11^2 = 121, so 1.1^2 = 1.21, and so 1.1 is a pretty good approximation to sqrt(1.2). If you need slightly better, but still cannot use a calculator, note that 1.1 is slightly high, and assume the right answer is 1.1-x. That gives (1.1-x)^2 = 1.2, which can be rewritten as x = 0.01/(2.2-x). If x is small, we can neglect it in 2.2-x, suggesting we look at x = 0.01/2.2. Let's approximate 2.2 with 2 to make the mental math easier, giving us x = 0.005. That gives us a new approximation for sqrt(1.2) of 1.1 - 0.005 = 1.095. That is quite close. It's square is 1.199025.
If you want an answer that works well under both the "it's for firmware" interpretation and the "it's for me and I don't have a calculator" interpretation is to use the binomial theorem. For square roots, that says sqrt(1+x) = 1 + x/2 - x^2/8 + x^3/16 - 5x^4/128 + ...
With x = 0.2, that's 1 + 0.1 - 0.005 + 0.0005 - ... Note that if you stop at 3 terms you get the same approximation I got earlier, 1.095. Four terms gives 1.0955. That's a good place to stop because 5 terms gets harder to do mentally because of that stupid 5/128.
Especially given modern computer tools, I'm actually not sure how many mechanical engineers would be able to derive that sort of thing in an interview. I wouldn't have been able to but you probably didn't want me designing rockets either.