The Flying Colours Maths blog has been running posts twice weekly since 2012, covering maths from the basics to… well, the most advanced stuff I have a clue about.
Here they all are, sorted by date. Some day, other ways to filter them will be possible.
The marvellous @solvemymaths tweeted some time ago about finding least common multiples and highest common factors: I broadly agree with Ed - I have an antipathy towards Venn diagrams that’s probably more fierce than they deserve. The tweet got me thinking about how I think about LCM and HCF …
In this, the final episode of WBU, @reflectivemaths and I discuss: @samuel_hansen’s antiracism post1. Dave and I both assert that Black Lives Matter and acknowledge that we have a significant amount of work to do to create a just society. In a whiplash-inducing change of tone, tooth fairy …
Dear Uncle Colin, I have been presented with this diagram: the marked points are a third of the way along the sides. I need to know what fraction of the grey square is shaded blue. Any ideas? Somehow Hued Area Defies Evaluation Hi, SHADE, and thanks for your message! There are several ways of doing …
Once upon a time, I was a sudoku fiend. They provided an outlet, a distraction, a hiding place – I could bury my head in one for, say, half an hour and whatever had been troubling me before was somehow less of an issue. It’s not an effective strategy for dealing with day-to-day living, but it was a …
Dear Uncle Colin, I have an octahedron, and I’m not afraid to use it! But I am afraid to find the angle between two adjacent faces. How would you do that? Protractors Lack Accuracy Tackling Octahedron Hi, PLATO, and thanks for your message! An octahedron is a shape made from eight equilateral …
Last week, the English Football League season was cancelled, with standings decided on a points-per-game basis in League One and League Two1 In League One, that led to Wycombe Wanderers leaping into the playoffs at the expense of Peterborough, who had accrued the same number of points but played a …
In support of #strike4blacklives, there is no Ask Uncle Colin today. Please see Shut Down STEM to learn more. I will be spending the time I would have spend working reading Superior by Angela Saini in an attempt to fill some of the gaps in my knowledge. Black lives matter.
It’s always fun to tackle a puzzle from one of Cav’s posts - in this case, a Catriona Shearer puzzle; it looks like my solutions are completely unrelated to his, although in reality I tend to sneak the odd peek and take some inspiration1 I also liked that Cav shared many of his failed attempts. I’m …
Dear Uncle Colin, How do I tell which is larger, $2^{-10^{-20}}$ or $1 - 2^{-10^{20}}$? - Unexpectedly Narrow Interval… Thank You! Hi, UNITY, and thanks for your message! As you’ve doubtless realised, both of those are “pretty much 1”. The question is, which is closer? As usual, there are several …
A second-in-a-row Dictionary of Mathematical Eponymy post about Boolean logic today – and another example of a Very Neat Diagram. What is a Randolph diagram? You’ve seen - at least, I hope you’ve seen - Venn diagrams. Beastly things. I would chuck them out the window if I could, they just don’t sit …
Dear Uncle Colin, Can two polynomials be equal everywhere in some non-trivial interval $[a,b]$ but not equal elsewhere? - Lacking A Good Reasonable Answer, No Good Explanation Hi, LAGRANGE, and thanks for your message! The answer is “no”, but to explain why, I need to give you a few pieces of …
A puzzle that came to me via @sheena2907: Choose two numbers, $x$ and $y$, uniformly from $[0,1]^2$. What’s the probability that $\frac{x}{y}$ rounds to an even number? What’s the probability that it rounds down to an even number? As always, spoilers below the line. Rounding One of my best …
Dear Uncle Colin, Is there a rigorous explanation of why the direction of the inequality changes when you flip the sign? - Fuzzy Logic, Inequality Puzzle Hi, FLIP, and thanks for your message! Here are my best efforts at a rigorous explanation; I’d be interested to read anyone else’s go at it! …
A nice thinker from Futility Closet: A rail one mile long is lying on the ground. If you push its ends closer together by a single foot, so that the distance between them is 5279 feet rather than 5280, how high an arc will the rail make? Feel free to have a go yourself! Spoilers below the line. …
In this, the penultimate episode of Wrong, But Useful, we’re joined by @karenshancock (who is Karen Hancock in real life). We discuss: A scoring system for an online quiz round. The Big Mathoff What is a surd? Currently reading Ratio by Michael Ruhlman - a cookery book that starts from the …
In this, the penultimate episode of Wrong, But Useful, we’re joined by @karenshancock (who is Karen Hancock in real life). We discuss: A scoring system for an online quiz round. The Big Mathoff What is a surd? Currently reading Ratio by Michael Ruhlman - a cookery book that starts from the …
Dear Uncle Colin, I’m trying to solve $\frac{x}{x-1} = \frac{1}{x-1}$. I think the answer should be 1, but my teacher disagrees. What do you think? - First Results Are Contradicting Teachers’ - Is One Nonsense? Hi, FRACTION, and thanks for your message! It’s tempting, here, to multiply both sides by …
This is an extended version of my entry in the Lockdown Mathoff at the Aperiodical Binet’s formula1 is a lovely way to generate the $n$th Fibonacci number, $F_n$. If $\phi = \frac{1}{2}\left(\sqrt{5} + 1\right)$, then $$F_n = \frac{ \phi^n - (-\phi)^{-n} }{\sqrt{5}}$$ Haskell and computation The …
Dear Uncle Colin, Why does $0! = 1$ and not 0? - Nothing Is Logical Hi, NIL, and thanks for your message! My best explanation for this - by which I mean, the one I can get some people to accept, goes like this: $4! = 4 \times 3 \times 2 \times 1 = 24$. To get to $3!$, you divide $4!$ by 4 and get …
There was a Fields Medallist named Dan Quillen, after whom are named several things in topics I’ve never head of. Other than Quillen, so far as I can tell, the only mathematical eponyms beginning with Q relate to Willard Van Ormine Quine. I know him from Godel, Escher, Bach, where his paradox was …
Dear Uncle Colin, I need to find a unit vector in the xy-plane that makes an angle of 45 degrees with the vector $3\bi + 4\bj$. How would you do that? - Don’t Enjoy Maths Of Integer Vectors Rotating Enough Hi, DEMOIVRE, and thanks for your message! I can think of several ways to approach this. …
A couple of puzzles that came my way via @srcav today: Cav’s solutions to this one are here; mine are below the line further down. And to this one, here Have a go yourself before you read on! I’ve mentioned before about @solvemymaths and @cshearer41 puzzles: they usually consist of two puzzles. …
Dear Uncle Colin These two trig questions are getting me frustrated! What do you recommend? Prove $\frac{\tan(2x) + \cot(x)}{\tan(2x) - \tan(x)} \equiv \cot^2(x)$ Prove $\frac{1 + \sin(2x)}{1+\cos(2x)} = \frac{1}{2}\left(1+\tan(x)\right)^2$ - I Don’t Like Equations Hi, IDLE, and thanks for your …
Over on Reddit, a couple of “last digit” puzzles crossed my path, and I thought I’d share the tricks I used, as much for my reference as anything else. 1. Show that the last digit of $6^k$ is 6, for any positive integer $k$. There’s a standard way to prove this using induction (it’s true for 6, and …
In episode 78 of Wrong, But Useful, we’re joined by @c0mplexnumber, who is Clarissa Grandi in real life. This month, we discuss: Clarissa’s Artful maths books, available via Tarquin - the activity book and the teacher’s guide Number of the podcast: $\phi$ (and 3D maths) …
Dear Uncle Colin, I need to find $35^{-1} \pmod {234}$, but I’m not getting the right answer. Can you help me?1 - It’s Not Very Easy Resolving Such Expressions Hi, INVERSE, and thanks for your message! We’re looking for a number $x$ such that $35x = 234n + 1$, for some value of $n$. My first …
What makes a mathematician a mathematician? Scientific studies say one thing above anything else: laziness1 We will go to extraordinary lengths to avoid doing any proper work. For example, I had a situation: I had two points - call them $P$ and $Q$ - and a line with the equation $ax + by + c=0$; I …
Dear Uncle Colin, I noticed that the incircle of a 3-4-5 triangle has a radius of 1, and for a 5-12-13 triangle, it’s 2. Is it always an integer in a Pythagorean triangle? Having Elegant Radius Or Not? Hi, HERON, and thanks for your message! It turns out that yes, the incircle of a Pythagorean …
“Lightly grease a 20x20cm baking tin with butter and spoon in the mixture. Press into the corners with the back of a spoon so the mixture is flat and score into 12 squares.” - BBC Good Food flapjack recipe by user nicolajlittle Hang on a minute - I thought, mid-baking. It doesn’t say what size …
Dear Uncle Colin, I need to find four consecutive numbers such that the first is a multiple of 5, the second a multiple of 7, the third a multiple of 9 and the fourth a multiple of 11. Can you find such a number? - Summing Up Needs Zero Intelligence Hi, SUNZI, and thanks for your message! There are …