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<div dir="ltr" data-setdir="false">Without spooling the fun and giving the answer, this problem was worked out in high school math class. Then we went around the large room and everyone gave their birthday. No matches. To be 100% sure of a match you need 366 people.<br></div><div><br></div>
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On Friday, March 27, 2020, 5:12:11 PM PDT, Rick Moen <rick@linuxmafia.com> wrote:
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<div>Quoting Texx (<a href="mailto:texxgadget@gmail.com" rel="nofollow" target="_blank">texxgadget@gmail.com</a>):<br><br>[pond puzzle:]<br><br>> Putting on sysadmin hat, the question should be asked WHY do they get this<br>> problem wrong?<br><br>The most common hypothesis is that people are so accustomed to _linear_<br>trends that they picture those even where you stress that this is<br>something dramatically different.<br><br>To elaborate on that, human intuition was shaped pretty well be natural<br>selection to avoid getting eaten on the savannah, but consistently<br>misleads people in a more-complex world.<br><br>Here's another puzzle to make the point: In a pre-SARS-CoV-2 scenario,<br>you have a room where a random assortment of people gather. How many<br>people must enter the room before there is a > 50% likelihood of at<br>least two of those people sharing the same birthday? Take a guess based<br>on intuition, and then I'll be glad to explain why your intuition on<br>this puzzle (_and mine too, and everyone else's_) is wildly wrong.<br><br>For simplicity, and to avoid getting all wound up in (uninteresting!)<br>edge cases, assume 365 days in the year (e.g., let's not get hung up on<br>Frederic from 'Pirates of Penzance' having been born on Feb. 29 and<br>apprenticed to pirates until his 21st birthday), and let's assume rates<br>of human birth are randomly distributed around the days of the year.<br><br>If you want to cheat, look up 'Birthday Paradox' -- or, if you're a<br>tedious math wonk, you can just calculate the answer. But doing either<br>of those does an end-run around my point, which is how very wrong<br>everyone's intuitive guess is, and why that happens. (Which I'll<br>explain later.)<br><br>Hint for the math wonks: The easy way to calculate the answer involves<br>inverting the question.<br><br><br>> If its doubling every day then going back a day its halving.<br>> That known, its quite easy to find 50% 25% 12.5% .625% etc.<br><br>Be careful: Like the epidemial concept of R-zero, the basic<br>reproduction number, doubling rate is _completely_ context-dependent.<br>It is not an inherent, fixed property of a disease organism, but rather<br>a value observed specific to a time and place that depends on local<br>conditions (including population density, part of the reason NYC is in<br>such trouble).<br><br><br><br>> Everyone NEEDS a LOG!<br><br>I'm not sure it did much for Margaret Lanterman.<br><a href="https://www.youtube.com/watch?v=BloTVTziM6c" rel="nofollow" target="_blank">https://www.youtube.com/watch?v=BloTVTziM6c</a><br><br><br>_______________________________________________<br>conspire mailing list<br><a href="mailto:conspire@linuxmafia.com" rel="nofollow" target="_blank">conspire@linuxmafia.com</a><br><a href="http://linuxmafia.com/mailman/listinfo/conspire" rel="nofollow" target="_blank">http://linuxmafia.com/mailman/listinfo/conspire</a><br></div>
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