Yesterday was 23/11, also known in some parts as 11/23, and you may recognise this as being a date made of the first four Fibonacci numbers. (Such numerical date-based Fibonacci coincidences haven’t been as exciting since 5/8/13, but at least this is one we can celebrate annually.) This meant that mathematicians everywhere got excited about #FibonacciDay, and spent the day talking about the amazing sequence. Here’s a round-up of some of the best bits, so you can celebrate Fibonacci day in style.

# You're reading: Blackboard Bold

### The Hidden Maths of Eurovision

Every year, the Eurovision Song Contest brings with it fresh accusations that the results are affected more by politics than music. But how much of the outcome is in fact determined by mathematics?

### Matt Parker talks percentages

If anyone caught BBC1’s consumer moanfest *Watchdog* this week, they may have been pleasantly surprised to see Aperiodicobber Matt Parker featured in the show. Following a segment about a UK sports chain and its shocking use of the classic ‘UP TO 70% OFF’ ruse, they invited Matt on the show to explain how to calculate percentages more easily, and so that Anne Robinson could mock him for being Australian, apparently.

Since the tips Matt presented were useful, we at the Aperiodical thought it was worth reproducing Parker’s Patented Percentage Ploys here, for your reference.

### How to solve a Rubik’s Cube in one easy step

**Note: **If you’re looking for instructions on solving Rubik’s cube from any position, there’s a good page at Think Maths.

One day some years ago I was sat at my desk idly toying with the office Rubik’s cube. Not attempting to solve it, I was just doing the same moves again and again. Particularly I was rotating one face a quarter-turn then rotating the whole cube by an orthogonal quarter-turn like this:

Having started with a solved cube, I knew eventually if I kept doing the same thing the cube would solve itself. But this didn’t seem to be happening – and I’d been doing this for some time by now. This seemed worthy of proper investigation.

### 3.142: a π round-up

‘Tis the season to celebrate the circle constant! Yes, that’s right: in some calendar systems using some date notation, the day and month coincide with the first three digits of π, and mathematicians all over the world are celebrating with thematic baked goods and the wearing of irrational t-shirts.

And the internet’s maths cohort isn’t far behind. Here’s a round-up (geddit – *round?!*) of some of our favourites. In case you were wondering, we at The Aperiodical hadn’t forgotten about π day – we’re just saving ourselves for next year, when we’ll celebrate the magnificent “3.14.15”, which will for once be more accurate to the value of π than π approximation day on 22/7. (Admittedly, for the last few years, 3.14.14 and so on have strictly been closer to π than 22/7. But this will be the first time you can include the year and feel like you’re doing it right.)

### Carnival of Mathematics #106 – December 2013

Happy New Year! And welcome to the first Carnival of Mathematics of 2014. The Carnival is a monthly roundup of blog posts on or related to mathematics, from all over the internet. Posts are submitted by authors and readers, and collated by the host, whose blog it’s posted on. This month, the Carnival has pulled in here at The Aperiodical, and we’re all ready with our party hats for the celebration of mathematical blogging that implies.

### From the Mailbag: Dual Inversal Numbers

*Katie, one of our editors, has been contacted by Brendan with a question about some maths he’s been investigating. Read on to find out what he’s discovered, and read Katie’s response.*

Dear The Aperiodical,

I’ve noticed an interesting property of numbers, and I wondered if you could tell me if this is something which is already known to mathematicians? I’ve been calling them Dual Inversal Numbers, but I’d love to know if they have an existing name, and if there’s anything else you can tell me about them.