How To Multiply By 365 In Your Head


Kevin Fagin’s Drabble from Sunday poses a nice bit of recreational mathematics, the sort of thing one might do for amusement: Ralph Drabble tries to figure how long he’s spent waiting at one traffic light. I want to talk about some of the mental arithmetic tricks I’d use to get through the puzzle without missing the light’s change. In the spirit of the thing I’m doing the calculations for this only in my head, though I admit checking with a calculator afterward to see if I got close.

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Some More Comic Strips


I might turn this into a regular feature. A couple more comic strips, all this week on gocomics.com, ran nice little mathematically-linked themes, and as far as I can tell I’m the only one who reads any of them so I might spread the word some.

Grant Snider’s Incidental Comics returns again with the Triangle Circus, in his strip of the 12th of March. This strip is also noteworthy for making use of “scalene”, which is also known as “that other kind of triangle” which nobody can remember the name for. (He’s had several other math-panel comic strips, and I really enjoy how full he stuffs the panels with drawings and jokes in most strips.)

Dave Blazek’s Loose Parts from the 15th of March puts up a version of the Cretan Paradox that amused me much more than I thought it would at first glance. I kept thinking back about it and grinning. (This blurs the line between mathematics and philosophy, but those lines have always been pretty blurred, particularly in the hotly disputed territory of Logic.)

Bud Fisher’s Mutt and Jeff is in reruns, of course, and shows a random scattering of strips from the 1930s and 1940s and, really, seem to show off how far we’ve advanced in efficiency in setup-and-punchline since the early 20th century. But the rerun from the 17th of March (I can’t make out the publication date, although the figures in the article probably could be used to guess at the year) does demonstrate the sort of estimating-a-value that’s good mental exercise too.

I note that where Mutt divides 150,000,000 into 700,000,000 I would instead have divided the 150 million into 750,000,000, because that’s a much easier problem, and he just wanted an estimate anyway. It would get to the estimate of ten cents a week later in the word balloon more easily that way, too. But making estimates and approximations are in part an art. But I don’t think of anything that gives me 2/3ds of a cent as an intermediate value on the way to what I want as being a good approximation.

There’s nothing fresh from Bill Whitehead’s Free Range, though I’m still reading just in case.

Fibonacci, a Comic Strip, and Venice


The comic strip Frazz, by Jef Mallett, touches another bit of mathematics humor. I imagine if I were better-organized I’d gather all the math comic strips I see over a whole week and report on them all at once, but, I’m still learning the rules of this blog, other than that anyone writing about mathematics has to bring up Fibonacci whether they want to or not.

The association that sequins brings up for me now, though, and has ever since a book I read about the United States’s war on the Barbary Coast pirates, is that the main coin of Venice for over 500 years of its existence as an independent republic was the sequin, giving me notions of financial transactions being all sparkly and prone to blowing away in a stiff breeze. It wasn’t that kind of sequin, of course or even any sort of particularly small coin. The Venetian sequin was a rather average-looking gold coin, weighing at least nominally three and a half grams, and the name was a mutation of “zecchino”, after the name of Venice’s mint. But, apparently, the practice of sewing coins like this into women’s clothing or accessories lead to the attaching of small, shiny objects into clothing or accessories, and so gave us sequins after all.

A listing on a coin collectors site tells me the Venetian sequin was about two centimeters in diameter, which isn’t ridiculously tiny at least. I’m not sure if that is a reliable guide to the size, although since it’s trying to sell me rare coins, probably it’s not too far off. Unfortunately most of the top couple pages of Google hits on “Venetian sequin coin size” brings up copies of Wikipedia’s report, which fails to mention physical size. An Ottoman sequin at the British Museum’s web site lists its diameter as 2.4 centimeters, but its weight at four and a third grams.