Bill Shillito @solidangles.bsky.social · 31/08/2026Which of these is named "Kiki", and which of these is named "Bouba"? 4152
Bill Shillito @solidangles.bsky.social · 05/06/2026Besides, arguments (1) and (2) work just as well to show that ...9999 (with "infinitely many nines" to the left) equals -1. How weird is that? 100
Bill Shillito @solidangles.bsky.social · 02/01/2026As my contribution to sharing subtraction strategies, here's how I do subtraction nowadays, using negative numbers! Made this up on the fly way back when I first started tutoring because I couldn't remember how to do multiple borrowing anymore and I never liked the lie of "you can't take 3 from 2". 2102
Bill Shillito @solidangles.bsky.social · 07/12/2025Students who take AP Statistics are 3x more likely to be able to tell the difference between correlation and causation. 310928
Bill Shillito @solidangles.bsky.social · 18/11/2025Which of these is an "A"? Why? #Grading Image source: www.mpusd.net/apps/pages/i... 030
Bill Shillito @solidangles.bsky.social · 21/10/2025This was the exact moment I learned it's called "maths" across the pond. 141
Bill Shillito @solidangles.bsky.social · 11/10/2025Ah yes, the four basic operations: addition, subtraction, checkmark, and multiplication. 3100
Bill Shillito @solidangles.bsky.social · 09/10/2025UGH, more mistakes that of course I only catch after posting ... here's the corrected graphic. One of these days I'll manage to post something completely right the first time. 😅 020
Bill Shillito @solidangles.bsky.social · 09/10/2025It turns out we can instead use the quadratic mean, aka the root mean square (RMS). Squaring makes all the deviations positive, and square rooting at the end gets us back to our original units. (BTW, here's a video on why squaring really is the best choice: www.youtube.com/watch?v=q7se...) [15] 220
Bill Shillito @solidangles.bsky.social · 09/10/2025Let's look at one more application. In statistics, we often want to describe not just the center but the spread of a data set. The first thing most people try is averaging the deviations — but the overs will always cancel out the unders and give zero. So what can we do? [14] 130
Bill Shillito @solidangles.bsky.social · 09/10/2025It turns out these are both examples of a more general idea called an "f-mean." Here's the basic idea: 1. Apply some function f to your data. 2. Find the arithmetic mean. 3. Undo f with the inverse function f⁻¹. The geometric mean uses f(x) = log x, and the harmonic mean uses f(x) = 1/x. [13] 140
Bill Shillito @solidangles.bsky.social · 09/10/2025Again, why did this work? Well, in physics, you learn that frequency and wavelength are inversely proportional. So can we do as follows: 1. Take the reciprocals of the data. 2. Find the arithmetic mean. 3. Undo the reciprocal with another reciprocal. That's the harmonic mean. [10] 140
Bill Shillito @solidangles.bsky.social · 09/10/2025It turns out we need to use the harmonic mean: flip the string fractions upside-down, add, and divide 2 (the number of values) by the result. So I have to place my finger to make the vibrating string 2/3 as long. (BTW, if you lightly touch here, you get what's called a "string harmonic!") [9] 130
Bill Shillito @solidangles.bsky.social · 09/10/2025When I used to play viola in high school (alto clef represent!) I tuned to A440. An octave up the A string (making it half as long) is A880, and a perfect fifth is E660. (Almost — more on that later.) Where should I put my finger to play that E? It's NOT halfway to the octave mark! [8, lol] 130
Bill Shillito @solidangles.bsky.social · 09/10/2025The trick is to use logarithms to extract the exponents! We do a three-step procedure: 1. Take logarithms of the value. 2. Find the arithmetic mean. 3. Undo the logarithm with an exponential function. What we get is the geometric mean. (Fun exercise: check this algebraically!) [5] 230
Bill Shillito @solidangles.bsky.social · 09/10/2025We can get a more reasonable estimate with what's called the geometric mean: multiply the values and take a root (here a square root, since there were 2 numbers). This gives a much better estimate — as you can check on Wikipedia. But why did this work? How would anyone think to try this? [3] 130
Bill Shillito @solidangles.bsky.social · 09/10/2025Let's start with ol' reliable: the arithmetic mean. The average. What it does is find the number that's in the "center" of a given data set by "redistributing" the sum evenly across all the values. But as anyone who's studied triangles knows, there may be multiple kinds of "center!" [1] 130
Bill Shillito @solidangles.bsky.social · 09/10/2025I've been thinking a lot about means recently! Probably some combination of (1) teaching our data analysis unit in our STEM 101 course at Oglethorpe and (2) all of @howiehua.bsky.social's great posts surrounding Mean Girls Day. I'd like to show how some of these various means are related. 🧵 [0] 2245
Bill Shillito @solidangles.bsky.social · 25/09/2025At least Italian hasn't caved though! They still use the long scale. The extra thousand becomes "-ardo" (borrowed from French) at the end of the word but it still is easy enough to understand. And the term "milione" makes sense: the "-one" suffix makes it "big thousand". Magnifico! (5/5) 110
Bill Shillito @solidangles.bsky.social · 25/09/2025But wait! If we use the "long scale" in British English, we get base million, with a sub-base of a thousand, with a sub-sub-base of ten! And everything makes sense! ...or at least that used to be what British English uses. Now they just use the short scale like Americans. Bummer. (4/5) 110
Bill Shillito @solidangles.bsky.social · 25/09/2025The new groupings we get are based on powers of a thousand: millions, billions, trillions, and so on. But isn't it weird how the prefixes don't seem to match up with the powers? It's off by one. It would be nice if "trillion" were 1000³, but nope, it's actually 1000⁴. Confusing isn't it? (3/5) 100
Bill Shillito @solidangles.bsky.social · 25/09/2025For comparison, Japanese is base "man" = ten-thousand (or perhaps we could say base myriad), also with a sub-base of ten. I remember how difficult it was to learn that "million" is "hyaku-man" (百万), which translates to "one hundred myriad". I had to completely reframe how I group numbers. (2/5) 200
Bill Shillito @solidangles.bsky.social · 25/09/2025Hot take: The English language is not base ten. It's base thousand. Sure, we write numbers using the Hindu-Arabic digits 0 through 9, but the way our language is structured groups numbers in powers of a thousand. If anything, we're sub-base ten. (1/5) 1183
Bill Shillito @solidangles.bsky.social · 03/09/2025Today's lesson in COR 314! Students learned how to count in Iñupiaq and write numbers using the Kaktovik numerals (as well as convert between base ten and base twenty). 🧮 Lots of discussion about how the way we're used to thinking isn't the only way to do things! 🙂 2123
Bill Shillito @solidangles.bsky.social · 14/03/2025Happy #PiDay! To celebrate, here's my favorite representation of π: as a position in the combinatorial game of Stacks. 0110
Bill Shillito @solidangles.bsky.social · 01/03/2025Something seems off about the Euler characteristic of this hush puppy. 021
Bill Shillito @solidangles.bsky.social · 16/01/2025Apparently this is now what I do for fun when I need a break from work. 😂 3140
Bill Shillito @solidangles.bsky.social · 01/01/2025This year's deviled eggs for #NewYearsEve! Left: Garlic deviled eggs (using toum!) Right: Ramen deviled eggs (made like onsen eggs but hard boiled) 270
Bill Shillito @solidangles.bsky.social · 16/12/2024About to take my final for Abstract Algebra (group and field theory). If this goes well it will be the *last* final I ever have to take. LET’S GO! 😎 1170
Bill Shillito @solidangles.bsky.social · 27/11/2024Presented without comment: The Thermograph of "oof". 060
Bill Shillito @solidangles.bsky.social · 24/11/2024Optimist: The cup is half full. Pessimist: The cup is half empty. Combinatorial game theorist: The cup is a win for Left, because she can take it to the zero cup. If Right moves, he will take it to the one cup. 1143
Bill Shillito @solidangles.bsky.social · 16/11/2024tfw you're really bad at a game but you refuse to give up 070
Bill Shillito @solidangles.bsky.social · 16/11/2024#TodayInMaths we showed how Bayes' Theorem is the math(s) behind both poker bluffing and medical tests! We also talked about the implications of false positives AND false negatives, the importance of non-stigmatizing language, and further application to law. Next week — Texas hold'em! 1151
Bill Shillito @solidangles.bsky.social · 12/11/2024For starters, here's the one that starts it all. (No I'm not going to go through every single diagram.) What kind of math book opens up with this? The best kind of math book. 262
Bill Shillito @solidangles.bsky.social · 12/11/2024I need to start interacting here more regularly, but I’m terrible at coming up with what to post… …so until I come up with something better, I’m going to start occasionally posting some of the bizarre and lovable diagrams from Winning Ways. Who’s game? 3162
Bill Shillito @solidangles.bsky.social · 11/11/2024Oh hey another trinity knot enjoyer! Represent! 😁 110
Bill Shillito @solidangles.bsky.social · 31/10/2023Just taught an entire 105-minute online Statistics lesson like this. 😂 The mouth even moves. Best impulse buy at Spirit Halloween ever. 🐺 080
Bill Shillito @solidangles.bsky.social · 19/10/2023A really handy use case for #ChatGPT as an educator: coming up with problem scenarios. I am *terribly* slow and uncreative at coming up with these, so ChatGPT has been an absolute godsend when it comes to generating practice problems for my Elementary Statistics class. 130