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How I Can Tell I Am A Huge Nerd - The Mad Schemes of Dr. Tectonic [entries|archive|friends|userinfo]
Beemer

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How I Can Tell I Am A Huge Nerd [Mar. 24th, 2011|11:42 pm]
Beemer
In the checkout line this evening, I was thumbing through Reader's Digest, reading the humorous interstitials. They had one labeled something like "ridiculous interview questions" that had the question "How many basketballs would fill this room?"

And I thought, that's not ridiculous at all. That's actually quite an interesting question. Not for the most basic answer, that's pretty trivial -- just guesstimate how many basketballs fit along each dimension and multiply -- but to see whether the candidate asks any interesting followup questions. Like "Hexagonal close-pack, face-centered cubic, or just stuffed in randomly?" Or "Should I assume we've removed the furniture first?" Or "Do you want to use inflated basketballs?"

(And because I was overcome by curiosity, Google & Wikipedia tells me that a regulation basketball is about 30" in circumference, or 9.5 inches in diameter, and that FCC and HCP have the same (optimal) density of ~74%, while random packing is more like 50-60%, with a limit of 64%. The More You Know!)

Yeah. This is my brain.
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Comments:
[User Picture]From: furrbear
2011-03-25 06:43 am (UTC)
odd that FCC and HCP have the same packing density.
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[User Picture]From: dr_tectonic
2011-03-25 07:02 am (UTC)
I thought so too, at first, but it turns out to be not odd at all because they're almost the same arrangement. In both cases you have planes of spheres in a triangular lattice, with each layer nestled into the hollows of the layer below it. It's just a question of whether the offsets from layer to layer go ABABAB or ABCABC.

Edited at 2011-03-25 07:06 am (UTC)
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[User Picture]From: pink_halen
2011-03-25 12:22 pm (UTC)
I knew you were a nerd when you used Interstitial in a sentence.
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[User Picture]From: dr_tectonic
2011-03-25 05:06 pm (UTC)
Oh, you knew LONG before THAT! ;)
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[User Picture]From: k8cre8
2011-03-25 02:23 pm (UTC)
My sister gets the Digest, and I'd not picked it up in ages, and I saw *exactly* that question, and thought the same thing. Admittedly, after the initial thought about how I'd approach answering the question, I didn't go look up a basketball's dimensions, but, yeah. In the end I concluded that the list of questions was largely not ridiculous, and so, the headline was, to me, a disappointment.
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[User Picture]From: sunsmogseahorse
2011-03-25 02:34 pm (UTC)
Just read this but I'm trying to figure out ... oh, wait, I got it. With hexagonal stacking each ball loses the dimension relative to 60° * its circumference. Liking things tidy, I just assumed this would be hexagonal :)
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[User Picture]From: dr_tectonic
2011-03-25 05:11 pm (UTC)
I found this diagram on wikipedia quite illuminating.
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[User Picture]From: dr_tectonic
2011-03-29 02:02 am (UTC)
D'awww, shucks! *blush*
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[User Picture]From: dpolicar
2011-03-25 03:56 pm (UTC)
If I didn't want the job, I would probably reply "That depends quite a lot on the size of your basketball."
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[User Picture]From: dr_tectonic
2011-03-25 04:54 pm (UTC)
That might well be one of my questions even if I did want the job.

I think a good interviewer would counter with something like, "Good point. Regulation NBA size. Go."
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[User Picture]From: dpolicar
2011-03-25 05:03 pm (UTC)
(nods) I wouldn't ask it for a job I wanted because I would expect most interviewers to treat it as evidence of being uncooperative.

That said, if someone actually gave me that response, I would pretty much have to update my evaluation of whether I wanted the job on the spot.

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From: walrusjester
2011-03-25 05:52 pm (UTC)
The most ridiculous interview question I've gotten was "Have you ever been in a fistfight?" I'm curious how you'd approach that one.

As an aside, that was in an interview for VR-1, so it's quite meaningful in hindsight.
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[User Picture]From: dr_tectonic
2011-03-25 06:06 pm (UTC)
I can't think of any answer other than "Uh... no."

Or maybe, "No. Why?"

Unless you're interviewing for a job as a bouncer, that one is a ridiculous question.
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[User Picture]From: arcticturtle
2011-03-29 01:35 am (UTC)
I'm trying to remember where I read that, oddly enough, random sphere packing is not well understood from a fundamental mathematical POV. As in, you can physically measure or simulate, but there's not a from-first-principles theoretical workup.

https://secure.wikimedia.org/wikipedia/en/wiki/Random_close_pack says "Experiments have shown that (random close pack) gives a maximum density of about 49-50%"

and I'd demote it to about 40% for basketballs, b/c their high-grip surfaces would hinder them moving around to find their optimal arrangement.

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[User Picture]From: dr_tectonic
2011-03-29 02:03 am (UTC)
Well, it really depends on how well you can shake your office building, now doesn't it?
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