# October, 2014

## $n$ maths blogs I often read

What does a blogger do when he has a stinking headache, no ideas, and a commitment to write a blog post? Of course! A lazy list post! Luckily, it’s a lazy list post that gives a shout-out to people whose stuff I enjoy, so it’s not all bad. News, roundups

## Probability and prediction

A reader asks: Is it easier to predict every game in the first round of a tournament1, or to pick the eventual winner? There's a competition run by Sky, which is free to enter; you win £250,000 if you correctly predict the scores in six Premier League games. It's free

## What percentage of numbers have a seven in?

Someone on the internet asks: What percentage of the natural numbers have the digit 'seven' in them? This is going to sound like a weird answer: it's 100%. I know, I know: you can point at 42 and 100 and 986,543,210 and 666,666,666,666,666 and at least a handful of others

## Wrong, But Useful: Episode 19

In this month's WBU spectacular: Big MathsJam is coming up - book quickly! The Relatively Prime Series 2 Kickstarter closes today. Donate quickly! Dave's got a chapter in a book - order quickly! Colin sails into the wind (virtually) Dave's moving house over half term: what maths are the movers

## The Mathematical Pirate and the Formula Triangle

The Mathematical Pirate took one look at the piece of paper attached to the dock. “They’re BANNING formula triangles?! By order of @srcav?!” He swished his sword around. “Let me figure out where he lives, I’ll show him.” “He lives… inshore, cap’n” said the $n$th mate. “It’s too dangerous.” “Can

## Using Anki to learn and revise

There's a constant refrain in the Flying Maths Classroom, these days, of "I can't quite remember..." Whether it's a trig identity or $21 \div 7$, the outbreak of amnesia in the quiet suburbs of Weymouth seems close to epidemic proportions. What can one tutor do, faced with an unstoppable tide

## How can I avoid mistakes?

A reader asks: I keep dropping marks in tests by making silly mistakes. Is that something I just have to get used to? Great question! I have, in a box of ancient relics upstairs, one of my GCSE mock papers. On the front of it is the number "100", scribbled

## An awkward inequality

Solve $\sqrt{|x|-3} > x-4$ Difficult, as the man said. Difficult, difficult, lemon difficult. It’s not that it’s tricky to solve it - it’s just… fiddly. Let’s start by drawing the graphs. The right-hand side is easy enough: it’s a straight line with gradient 1, through the point $(0,-4)$. The left-hand

## 277.42 reasons why we shouldn’t readopt the imperial system

“We do these things… not because they are easy, but because they are hard.” - John F. Kennedy I love a challenge. I go out of my way to do Hard Sums in my head, in the hope of one day matching the Mathematical Ninja’s prowess. I run long distances.