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According to the Norwegian meterological institute, the answer is that it is best to run. According to Mythbusters (quoted in the comments to that article), the answer is that it is best to walk.

My guess would be that this is something that can be properly modelled mathematically and solved. I suspect that I'm not alone in making a start on this, but as it's usually during a rainstorm that I think of it, I don't get far before deciding that the best strategy is to call a taxi!

I would also guess that someone has already done this and figured out the answer. If I'm right about that, I would like to read about it and learn what the real answer is. Thus my question is most likely: can someone provide a reference for this?

(If I'm wrong that it's already been solved, then some pointers as to how to solve it or even an explanation of what the main issues are, would be most interesting.)

As well as simply satisfying my curiosity, this is also one of those questions that non-mathematicians often ask (or at least, that non-mathematicians can easily understand the motivation for the question) so if there's a reasonable answer then it would be a good way to show off some mathematics.

Update This question has a long and curious history. There's a discussion about it at the meta site: http://meta.mathoverflow.net/discussion/90/question-about-walking-in-the-rain

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7 
 Andrew, I'm voting this down to register my preference: this kind of question is not what I want MO to be for. Of course that's just my personal taste. It would be different if you'd put up evidence that there was interesting mathematics to be found here. – Tom Leinster Nov 18 2009 at 12:50
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 @Tom (and Scott): That's precisely my question! Is there any interesting maths here? (But I have no quarrel with the down votes, I'm still trying to work out what makes a "good" question, since my research-level ones tend not to get answered!) – Andrew Stacey Nov 18 2009 at 16:15
51 
 I find this strange. What's so bad about Andrew's question? A questiomn that has as an answer a full-fledged math article that at least 7 people so far indicate is useful can't be that bad. What is off-topic here? The fact that the question involves high-school math? Are questions involving high-school math off topic here? They can still be pretty hard to answer! I find there are plenty of questions on the forum that are not as suitable as this one. Puzzles me. – Urs Schreiber Nov 18 2009 at 18:20
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 And besides: this down-voting of people who one can just as well reasonably talk to is something I find rather irritating and unworthy of a forum for what should be grown-ups. – Urs Schreiber Nov 18 2009 at 18:21
25 
 I also do not see why this question was closed. I think this is a very interesting question, one that I ("a full-time mathematician") have wondered about many times myself. From the article referenced in the answer below, we see that, although it is perhaps clear that the question only requires basic calculus, the question is still a fairly non-trivial one. – Kevin Lin Nov 18 2009 at 19:11
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closed as off topic by Scott Morrison♦ Nov 18 2009 at 17:00

2 Answers

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try this, the latest in a long line of recreational mathematics on the topic

"Keeping Dry: The Mathematics of Running in the Rain" Dan Kalman and Bruce Torrence, Mathematics Magazine, Volume 82, Number 4 (2009) 266-277

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 The article is available online here: stanwagon.com/public/TorrenceRainMathMag.pdf – Kevin Lin Nov 18 2009 at 19:03
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 Also, this very same question is the subject of the following article - sputnik.master-telecom.ru/Seans/Kvant/1989/03/… - in Kvant, which is a sort of Russian recreational mathematics magazine. I don't know if an english translation is available. – alex Mar 15 2010 at 2:49
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 That first link is now dead; the article is at www1.math.american.edu/People/kalman/pdffiles/…. – joriki Aug 7 at 14:21
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This is a completely spurious answer designed purely to test a bug.

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 What bug are you testing? The ability to answer a question which has already been closed? – sleepless in beantown Sep 3 2010 at 12:51
That's the one. Meta thread: <meta.mathoverflow.net/discussion/644/…; – Andrew Stacey Sep 3 2010 at 13:08
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 +1 for a great bug-find – Cam McLeman Sep 3 2010 at 19:54
perhaps your high score of 9919 (currently) allows you to insert your comments onto pages which we mere mortals cannot modify! I don't have an Add Answer button on this page, but I've got three Add Comment links: one for the question, and one for each of the answers. Since I can't post on the moderator site, let me point out that this question being bumped up on the front page and its most recent submission coming from someone with >9k reputation is what made me come look at the site. It's strange that people are allowed to add comments, also. There's another bug which I cannot fit insi – sleepless in beantown Sep 3 2010 at 21:02
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 also, in client-server interactions, never ever trust the client. Always verify and validate all client-side entries. The fix for this ought to be to not allow any answers on closed questions from the server side also. – sleepless in beantown Sep 4 2010 at 0:28
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