# Wrong, But Useful: Episode 15

It's the (slightly delayed) monthly chat between @reflectivemaths (Dave Gale) and me on whatever maths has caught our eyes.

This month:

• Why protractors and set squares? You can find centres of rotation.
• Why constructions? Colin launches an impassioned defence and compares them to Killer Sudoku
• Dave has some great ideas for improving the Mathematical Instruments package, while Colin wants to shake up the calculator industry
• Exams: do you deserve full marks for a lucky guess? Neither of us think so, but the GCSE disagrees. Outrage ensues, before Dave suggests not ranting about exams yet again.
• Dave goes shopping for horse-balls but only finds confusingly-priced pizza [link]. We fail to discuss the density of prawns. Colin suggests the reason is 'economics'. Dave brushes this off. Dave is unhappy about the convention in some puzzles that A=1, B=2 and so on1 but Colin thinks he's being oversensitive.
• Stephen Hawking lets the side down with a Perfect Formula. Even for charity, even with some actual statistics behind it, that's a case for the Maths Police.
• Dave interrupts the football commentary with a super-relevant query: is half a million chickens a lot to rehome2 ?
• Colin's reading: Dead Reckoning by Ronald Doerfler, which has inspired him to try to do 1/97 in his head (it's 0.010309278350515463... - he could go on, but your calculator couldn't.)
• The World Cup seeding system: how England, Holland and Italy managed to fall foul of it by picking silly friendly opponents.
• Dave interrupts the football commentary again to explain that that last month's answer was $\frac{5}{11}$; gold stars to @srcav and @notonlyahatrack
• This month's World Cup puzzle:

How many possible World Cup tournaments are there? There are 32 teams in eight round-robin groups (each with six games, each of which has three possible results) and 16 knock-out games (each with two possible results). We're not interested in the actual number: just how many digits long it is.

• Colin doesn't understand Graham's Number and isn't really sure how to say 'Knuth'

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* Updated 2014-09-21 to fix a link.

## Colin

Colin is a Weymouth maths tutor, author of several Maths For Dummies books and A-level maths guides. He started Flying Colours Maths in 2008. He lives with an espresso pot and nothing to prove.

1. which I'm not going to typeset in LaTeX because it's NOT ALGEBRA []
2. Possibly on the other side of the street. []

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