# November, 2017

## Ask Uncle Colin: Winning the Lottery

Dear Uncle Colin, Can you help me win the lottery using MATHS!? - Lots Of Time, Tremendous Optimism No. I mean, there's a chapter in The Maths Behind1 on exactly that topic, but honestly? If I knew how to win the lottery, I'd be drinking mocktails on a Caribbean beach

A charming little puzzle from Brilliant: $x^2 + xy = 20$ $y^2 + xy = 30$ Find $xy$. I like this in part because there are many ways to solve it, and none of them the 'standard' way for dealing with simultaneous equations. You might look at it and say

## Ask Uncle Colin: Evil in integral form

Dear Uncle Colin, I've been set an evil integral: $\int_0^\piby{4} \frac{\sqrt{3}}{2 + \sin(2x)}\d x$. There is a hint to use the substitution $\tan(x) = \frac{1}{2}\left( -1 + \sqrt{3}\tan(\theta)\right)$, but I can't see how that helps in the slightest. -- Let's Integrate Everything! Hello, LIE, and thank you for your message!

## Long division

Some time back in the olden days, @robeastaway posted this: My 11 year old's sample SATs papers found in his book bag. "Work out 1118÷43 (no calculator)." I wish all ministers had to take these tests. pic.twitter.com/dEOiLv2fsJ — Rob Eastaway (@robeastaway) March 22, 2017 Before I say anything else: I

## Ask Uncle Colin: I keep forgetting stuff!

Dear Uncle Colin, I'm revising for a high-stakes exam. I learn material, do the exercises and think I understand it - but when I revisit it a couple of weeks later, it feels like I'm starting from scratch. What can I do to remember things better? -- Failure Of Remembering

## Wrong, But Useful: Episode 50

This month's episode is the 2017 MathsJam special. What we talked about: Some tables Some talks we liked (featuring @reflectivemaths, @ajk_44, @zoelgriffifths (of whom more later), @macaronique, @chalkdustmag, @pecnut, @mscroggs, @televisionduck, Andrew Russell) Dave talks to @pecnut about his favourite bits, how to dress to give a lecture, Catchphrase1, oblongs,

## Another of Colin’s blasted puzzles

Before I begin: this post involves a puzzle and my attempt at a solution; everything above the horizontal rule is spoiler-free, but go beyond that at your peril. Some days, you can almost hear @colinthemathmo's chuckle as he innocently poses a question such as: Find all configurations of 4 points

## Ask Uncle Colin: Oh God, Not This Again

Dear Uncle Colin, When evaluating an expression, after you've dealt with brackets, powers and roots, do you deal with multiplication and division left to right, or does multiplication take precedence? - BIDMAS Idiocy Doesn't Make Any Sense Hi, BIDMAS, and thanks for your message! There are three answers to this.

## On the obelus

Recently, @solvemymaths asked the rather leading question: is there a convincing argument for ever using the obelus (÷) for division rather than fractional notation? In my mind it makes things harder — solve my maths (@solvemymaths) June 16, 2017 As with pretty much all mathematical notation questions, I have exactly

## Ask Uncle Colin: Impulse and Speed

Dear Uncle Colin I have a conceptual problem with impulse. Suppose you have a collision where your particle (of mass 1 kg) has an approach speed of 4m/s, changes direction, and leaves with a speed of 3m/s. That's an impulse of -7 units, and the ball slows down from 4m/s