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Books of the Year 2020

For the first time, I’ve been using Goodreads to track what I read, and making sure to read a bit at bedtime almost every night. I figured it would be worth listing the books that I felt were five-star books, in case they help anyone else. In alphabetical order by

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A Catriona Shearer Classic

If you’ve read this blog for a while, you’ll know I’m a fan of @cshearer41’s puzzles (her book, Geometry Puzzles in Felt Tip, is available wherever etc). At a recent MathsJam, one jumped out of Chalkdust at us: (Image from Issue 10 of Chalkdust, a magazine for the mathematically curious.)

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Dictionary of Mathematical Eponymy: The Lutz-Nagell Theorem

One of the reasons I’m writing the Dictionary of Mathematical Eponymy is to introduce myself to new ideas, and to mathematicians I didn’t know about. To things I wish I knew more about. Elliptic curves are pretty high on that list. What is the Lutz-Nagell theorem? It’s sometimes - reasonably,

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A double tangent

A puzzle via @CmonMattTHINK (Matt Enlow): There is a line that is tangent to the curve y = x^4 - x^3 at two distinct points. What is its equation? (Can you find it without calculus?) #iteachmath #math #maths #mathchat #mathschat — Matt Enlow (@CmonMattTHINK) December 21, 2018 (I think we

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The Mathematical Ninja and the Ninety-Sevenths

“A ninety-seventh.” The student scratched her head. “I’d call that 0.01.” A moment more’s thought. “0.0103? Probably good enough.” For the Mathematical Ninja, this was about as good as could be expected. They sighed all the same and wrote down: $0. \dot 01\, 03\, 09\, 27\, 83\, 50\, 51 \\

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The Mathematical Ninja and the Other Rope

This is based on a puzzle I heard from @colinthemathmo, who wrote it up here; he heard it from @DavidB52s, and there the trail goes cold. The Mathematical Ninja lay awake, toes itching. This generally meant that a mission was in the offing. Awake or dreaming? Unclear. But the thought

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Ask Uncle Colin: Platonic Solids

Dear Uncle Colin, Why are there only five platonic solids? - Pentagons Look Awful. Try Octagons! Hi, PLATO, and thanks for your message! A platonic solid is a three-dimensional shape with the following rules: Each face is the same regular polygon The same number of edges meet at every vertex

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The Maths Behind The Errors In The Maths Behind

I recently had a flurry of correspondence with translators of The Maths Behind (available wherever etc., but also soon in Swedish and Korean): embarrassingly, they had caught several mistakes in the book. These things happen; we try to put them right and move on. However, it got me wondering: can

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Ask Uncle Colin: A Polling Percentage

Dear Uncle Colin I have a percentages problem: I'm told that in an election, 95.74% of the electorate voted for the winning side. What is the minimum possible size of the electorate? - Percentages Often Lack Logic Hi, POLL, and thank you for your message! There are two possible answers

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