Fraction Mnemonic

Table Illustrating how to easily remember percentages from fractions
When I tell people that I have a degree in Mathematics, often they expect me to be good at mental arithmetic. Nothing could be further from the truth. And that’s fine, because in Mathematics (and also in its more practical subdomain, computer programming, where I’ve spent over a decade working) one rarely deals with things like sums and products of literal numbers.

I am the last person you want calculating how to divide the bill at a restaurant.

But now that I’ve started this Boardcrafting business, I find myself routinely thrust into dealing with the sticky realities of numbers. Not the austere theoretical kind, but those vulgar, base-ten digits found at the bottom of receipts, on the marks of a ruler, in the cells of spreadsheets, lists of inventory, supplier quotes, tax rules, etcetera.

So in order to speed up my digestion of this new diet, I’ve started using the fibre of mnemonic tricks. But of course, I couldn’t make it easy on myself by finding popular shortcuts already out there, I must invent my own.

I have found myself often converting the fractions between 1/10 and 1/2 to percentages. Above you can see an illustration of my newly-adopted approximation method. Having lived in countries with coins in the 50, 25, and 20 cent denominations, 1/2, 1/4, and 1/5 are immediate for me. 1/3 and 1/8 have also been memorized for a while, but are shown here for completeness. For 1/6, I just take the six and put it after a one for roughly 16% (or 16.6-repeated, if one wishes to memorize a more accurate conversion). For 1/7, I just take the seven, multiply it by 2 and get 14% (multiply it by 4 to get “28”, the next couple digits). For 1/8 and 1/9, just subtract the denominator from 20 to get 12% (very rough) and 11%, respectively.

Quite a tangent from the usual Boardcrafting discussion, I know, but for those truly curious about how the sausage is made, you have to go inside the noodle.

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