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Comment by cntainer | Hacker News Reader

add 6 feet to a rope around the world, stretch it out and how far off the ground would it be

is this a technical puzzle/question? to me it reads like a middle school geometry question. it would be fun to discuss it with friends/colleagues but I wouldn't expect it during a software engineering interview

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https://mathimages.swarthmore.edu/index.php/Rope_around_the_...

> Although finding the answer requires only basic geometry, even professional mathematicians find the answer strangely counter-intuitive.

I guess the more a visual person you are the more counter-intuitive it is. That only 6 feet of rope is needed to widen the radius of Earth at every place at continents and oceans ect at a whole 1 feet seems crazy to me.

sure, the answer might seem counter-intuitive but the method to find the answer is not, as long as you know the connection between a circle's circumference and its diameter

I still fail to see how this is relevant for a technical interview, assuming that we're trying to hire a software engineer. Fun, but not relevant.

Hah, I just did the math on this myself, found the answer to be 0.955 feet, and assumed I had done something wrong, or was off by a factor (or two or three) of ten.

That is unexpected!

It helps me to think about it in opposite terms. You're increasing the radius by ~1ft (radius around the whole earth), and 2pi is the linear relationship with circumference, so you'll get six ft. Thinking about it this way kind of ignores the fact the circle is huge. I'm not too visual of a person though.

I think that's perhaps a naive interpretation. At the core of this question are a number of assumptions, and concepts to think about:

  - What is the rope made of? How stretchy is it? How strong is it to tensile stresses?

  - What model of the earth are we using? A sphere (circular cross-section?) ellipsoid? Which axis of the ellipsoid? Does it take terrain into effect, or just gravitation? How does the rope avoid hitting terrain?

  - How does the rope stay suspended? how does it resist gravity? are there uniform thrusters on it? How are they fueled?

  - How is length added to the rope? Is it stretched somehow? Material added? How is the added material, if applicable, inserted?

Ultimately, I think we need to know what project requirement is driving the question to be able to answer this. It would shed light on most of these assumptions. If it sounds like I'm being pedantic or overthinking the question, I'd disagree: These considerations are critical to giving a meaningful answer; otherwise the question doesn't make sense. Unless we're talking platonic forms or w/e.

It does sound like overthinking to me, but context is king. Without context/requirements we're just guessing.

Maybe the job interview is for Space X and they're working on some new system of mini-satellites-on-a-rope called Hyper-rope, or maybe google is trying to pivot their failed Loon project into some kind of air-born connectivity solution, and the rope is actually a very long fiber-optic cable.

Or the interview could be for an online eCommerce platform and the person being interviewed will most likely have to work in a huge heterogeneous codebase with all the important technical decisions already made.

otherwise the question doesn't make sense Well that is my point. I love these types of subjects, but when I'm having a beer with friends and we find a puzzle like this one and we try to take it as far as possible without going into fiction/bullshit territory.

So it could be useful to check/signal for culture fit, and in OP's case it actually worked like that OP: "We value people that love to get into this type of discussions/arguments" Interviewee: "Gosh, you guys bored me to death during the technical interview but it seems like we have similar tastes when it comes to theoretical puzzles so I'll give you another chance"

Nothing wrong with this though. It just proves that interviewing is a complex process and actual merit and success are highly subjective.

That's just the first question.

The follow-on is, if you add 6 feet and put your finger under the rope and pull up until it's tight again, how far have you raised your finger? 1ft? 10ft? 100ft? 1000 miles?

The answer to that is very difficult. There are several approaches.

I solved a very similar problem (in the context of a pathfinding and obstacle avoidance sim) 25 years ago, and I can probably describe the thought process and geometry in very digestible terms, but if I had to code it in a whiteboard I'd likely fail.

Same here. I don't code with somebody looking over my shoulder. Can't perform that way. :)

Yes, but that's still a geometry problem. Don't get me wrong, geometry was my favorite branch of mathematics in school, but I don't see how this is relevant for most software engineering jobs.

I guess this type of question might serve the purpose of finding like-minded people with similar interests (in your case geometry or puzzles) but it might alienate others.

Most folks require calculus to solve it. Give it a try!

great, now I need a new branch of math to be able to continue, lol!

An issue is that one person's trick question is another's straightforward problem. My college algebra students thought that every problem was a trick question, and that the only strategy for passing exams was memorization.

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