The Dreadful Truth About The Table of Joy

"But I don't liiiiike fractions," said the student. He also didn't like the look of the poker in the Mathematical Ninja's hand, which was beginning to glow red.

"Sure you do," said the Mathematical Ninja.

"Do I?"

"How do you do percentages?" He swished the poker around a bit, as if he was Yoda.

"Table of Joy."

"How do you do ratios?"

"Table of Joy."

"How do you work out pie chart angles? Currency conversions? Distance conversions?"

"Are you going somewhere with this line of questioning?"

But of course

The Mathematical Ninja put down the poker and picked up a pen. He sketched out a Table of Joy on the whiteboard. "15 miles to kilometres," he said. "5 and 8 in the top row. 15 and $x$ in the bottom."

The student nodded, bored. "So it's $15 \times 8 \div 5$, yeah, yeah."

He then wrote alongside it: $\frac {5}{15} = \frac{8}{x}$.

"But I don't like..."

"You're lucky, my friend, that my writing hand is the same as my poker-wielding hand. Multiply both sides by $15$ to get $5 = \frac{8 \times 15}{x}$. Multiply both sides by $x$ to get $5x = 8 \times 15$. Divide both sides by $5$ to get $x = 8 \times 15 \div 5$."

"That's the same..."

"All that time you were doing the Table of Joy? You were really doing algebra with fractions."

"Noooooooo!" said the student. He'd have preferred the poker.

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.

Share

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Your email address will not be published.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