### Wherein CP does that exam problem with the crocodile

This morning, Twitter was doing its Twitter thing about a maths problem again. Most people were linking to this BBC story, “Crocodile maths question ‘was challenging'”.

Apparently this year’s Scottish New Higher maths exam contained a question which a lot of people found hard. You could remove the word “crocodile” from that headline and obtain a perfectly acceptable statement about a maths exam, but that’s not what people are complaining about.

### What I did on my summer holidays

This summer my wife and I went to America on our honeymoon. We had a lovely time – it was hot, we saw stripey flags in all sizes, and we marvelled at what substances count as “food” in the land of the free.

But what I really want to tell you about is the National Museum of Mathematics in New York. We couldn’t fly all the way to the East coast of America and not pay a visit. So we did!

### Take the 30 second arithmetic challenge

My wife’s grandmother is a fearsome character. She’s in her nineties but still has all her wits about her. In fact, she’s got more than her fair share of wits. Whenever we visit her, she hits me with a barrage of questions and puzzles collected from the last several decades of TV quiz shows and newspaper games pages. My worth as a grandson-in-law is directly proportional to how many answers I get right.

One of her favourite modes of attack is the “30 Second Challenge” from the Daily Mail. It looks like this:

I decided it would be a fun Sunday morning mental excursion to make a random 30 second challenge generator

### I’ve made my own numbers-in-a-grid game

For the past couple of weeks, I’ve been obsessively playing the game Twenty on my phone. The fact that my wife has consistently been ahead of my high scores has nothing to do with it.

The main source of strife in my marriage.

Twenty is another in the current spate of “numbers-in-a-grid” games that also includes Threes, 10242048 (and its $2^{48}$ clones), Just Get 10, and Quento.

The basic idea is that you have a grid of numbered tiles, and you combine them to build up your score. While there are lots of unimaginative derivatives of the bigger games, there’s a surprisingly large range of different games following this template.

With so many different games being created, I thought that a chap like me should be able to come up with a numbers-in-a-grid game of my own. Yet, for a long time, I just couldn’t come up with anything that was any good.

Yesterday I had a really nice shower, and the accompanying feeling that I’d come up with a really good idea – make a game to do with arithmetic progressions.

### #thatlogicproblem round-up

C: $K_A m; \\ K_B d.$

A: $\neg K_A d; \\ m \vDash \neg K_B m.$

B: $d \not\vDash K_B m; \\ (K_A(\neg K_B m)) \vDash K_B (m,d).$

A: $m \wedge K_B(m,d) \vDash K_A (m,d).$

Albert, Bernard and Cheryl have had a busy week. They’re the stars of #thatlogicproblem, a question from a Singapore maths test that was posted to Facebook by a TV presenter and quickly sent the internet deduction-crazy.

First of all: no, it’s not meant to be answered by an average Singaporean student. It’s a hard question from a schools Olympiad test.

### I bought three.onefouronefivenine.com

I’m a big fan of novelty domain names: I once bought hotmathematicians.com just so that christian@hotmathematicians.com could be my corresponding address when I submitted a paper. That domain has expired, but my love for one-shot novelty purchases has not!

To celebrate π day this year, I decided that it should be possible to type a little bit of π into the internet and be given the rest of it. You can have dots in domain names, so a domain like “three.something.com” is possible. I only know π to two decimal places off the top of my head, so I was dismayed to learn that onefour.com is being squatted.

After a bit of googling to find more digits of π (hey, this website will be really useful once I set it up!), I found the first decimal approximation which hasn’t already been registered:

### three.onefouronefivenine.com

Try going there now. It really exists!

I’ve set it up so you get an endlessly scrolling list of decimal digits of π, generated using my favourite unbounded spigot algorithm. I suppose you can consider this my entry in our π approximation challenge.

A good π day’s work.

### Wolfram|Alpha can’t. But CP can!

For a while, I’ve been following this cool Twitter account that tweets questions Wolfram|Alpha can’t answer. The genius of it is that the questions all look like things that you could half-imagine the solution algorithm for at a glance, and many of them look like the kinds of questions Wolfram like to give as examples when they’re showing off how clever their system is.

Questions like this:

The answer to that is 278. How do I know that? I know that because I went on a little problem-solving binge answering the questions that Wolfram|Alpha can’t.