# You're reading: cp’s mathem-o-blog

### What I’ve done this year

I gave a talk at the big MathsJam conference at the start of this month. It happens annually, so I had a whole year to come up with something interestingly mathematical to entertain my fellow mathmos.

When it came time to decide on a topic, I realised I’ve done loads of stuff this year! It was really hard to choose. So, now MathsJam is over, I thought I’d collect together all the mathematical things I’ve done in the last 12 (-ish) months.

### Ask Clever Hans a question

I’ve put a very clever horse on the internet. He’s called Hans and I’ve made a little video about him.

You can ask Clever Hans your own questions! Go to christianp.github.io/clever-hans and make sure your microphone is turned on. Another proviso: I think only Google Chrome supports the special technology I used to make Hans work. Sorry!

I’ll explain how Hans does his horsey magic below the fold.

### 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:

You start with the number on the left, then follow the instructions reading right until you get to the answer at the end. It’s one of Grandma’s favourites because it’s very hard to do in your head when she’s just reading it out!

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.