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The maths of the Grime Cube

Not content with already having five cubes named after him, internet maths phenomenon James Grime has now developed a new Rubik’s cube-style puzzle for internet maths joy merchants Maths Gear. I’ve been slightly involved in the development process, so I thought I’d share some of the interesting maths behind it.

Another name for a Rubik’s cube is ‘the Magic Cube’ – and Dr James Grime wondered if you could make a Magic Cube which incorporates its 2D friend, the Magic Square.

A more equitable statement of the jealous husbands puzzle

Every time I use the jealous husbands river crossing problem, I prefix it with a waffly apology about its formulation. You’ll see what I mean; here’s a standard statement of the puzzle:

Three married couples want to cross a river in a boat that is capable of holding only two people at a time, with the constraint that no woman can be in the presence of another man unless her (jealous) husband is also present. How should they cross the river with the least amount of rowing?

I’m planning to use this again next week. It’s a nice puzzle, good for exercises in problem-solving, particularly for Pólya’s “introduce suitable notation”. I wondered if there could be a better way to formulate the puzzle – one that isn’t so poorly stated in terms of gender equality and sexuality.

James Grime’s house-building problem

Aperiodipal James Grime has put a new video on his YouTube channel. He’s got a problem to do with building houses:

But James posts fantastic videos about maths puzzles all the time; what’s so notable about this one?

I was involved, that’s what! The puzzle can be done on pen and paper but it involves a lot of drawing and calculating, so James asked if anyone could make a computery version. I spent my day off work last week making just such a thing: the computerised Building Houses Problem.

3.142: a π round-up

Pi pie by Robert Couse-Baker. Photo used under the CC-BY 2.0 license.

π pie by Robert Couse-Baker. Photo used under the CC-BY 2.0 licence.

‘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.)

Maths and Magic on BBC Radio 4

BBC Radio 4 put out a rather nice 30-minute documentary on the links between maths and magic recently. In Maths and Magic, Jolyon Jenkins explains a couple of simple algebraic ‘mind-reading’ tricks, before talking to various magicians and mathematicians in search of a mathematical trick that doesn’t ‘look’ mathematical. Regular readers of this site will recognise a few of the mathematicians featured in the programme.

I’m now a bit miffed that I managed to miss Jolyon at the big MathsJam in November, because the trick he ends with is the easy version of the de Bruijn trick that David and I made better last year.

Listen: Maths and Magic on BBC Radio 4.