The Mathematical Ninja And The Driving Awareness Course

“What are you doing here?”

“Never mind that, sensei, how on earth did they catch you?”

“... I don’t want to talk about it. In any case, I was only doing 5% more than the speed of light.”

“Yeah, that poses more questions than it answers, in honesty.”

The Powerpoint slide had the car coming to a stop from 30mph just in time to avoid hitting Tommy, the six-year-old chasing his ball into the road.

“Now,” said the instructor, “what if you’d been doing 32 instead? How fast would you hit Tommy?”

The dozen or so people on the driving awareness course muttered a bit. “Two” was a common answer. “32”, said someone who clearly wasn’t listening.

“Eleven,” said the Mathematical Ninja, confidently. “11.136 or so.”

The instructor raised her eyebrows and asked how he’d come up with that. She really didn’t realise what she was getting into.

“Kinetic energy, square law, yadda yadda yadda. $v^2=u^2 - 2as$, if that’s your cup of tea. In any case, the final speed here is the square root of $32^2 - 30^2$.”

“... I really don’t see how that...” Luckily, the instructor was a police officer and the Mathematical Ninja figured that one lot of trouble was enough for today1.

“$32^2 - 30^2$ is $62 \times 2$, by difference of two squares, or 124. That’s a smidge more than $11^2$, and the error is about $\frac{3}{22}$. That’s $\frac{14}{22} - \frac{11}{22}$, which is 0.63 recurring less a half, making 0.136. Give or take.”

The instructor tried very hard not to make a face, and moved on to the next slide without any further comment.

The Mathematical Ninja, meanwhile, looked to camera and sternly advised readers to watch their speed.


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. While the Mathematical Ninja respects regular law enforcement, they have no such qualms about the physics police since they became a freemeson. []


2 comments on “The Mathematical Ninja And The Driving Awareness Course

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up for the Sum Comfort newsletter and get a free e-book of mathematical quotations.

No spam ever, obviously.

Where do you teach?

I teach in my home in Abbotsbury Road, Weymouth.

It's a 15-minute walk from Weymouth station, and it's on bus routes 3, 8 and X53. On-road parking is available nearby.

On twitter