Forget The Basics, Tell Us Your Most Mind-Blowing Math Trick

I'm a writer by trade, and for some reason that means I'm OK at English and just plain bad at math.

A woman gesturing, with text "Math is worthless in real life."

Which means I rely on little math tricks to get me by.

Person reviewing financial documents next to a laptop and calculator, focusing on task at hand

Unrecognizable person counting expenses on calculator in mobile phone app, checking her energy bills at home. Budget management, price increases, inflation, rise in price of products and utilities. View from above, managing home finances using smart phone

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For example, I tip 20% everywhere just because I know 20% is moving the total's decimal over one number to the left, then doubling it.

For example, a 20% tip on a $63.00 bill is $12.60 ($6.30 x 2 = $12.60).

And if I'm multiplying any number by 5, just half said number and plop a zero at the end.

So 5 x 12 = 60 (half of 12 is 6, then add a 0).

I only have two, so now I want to know if you have a quick math trick you live by that makes life a heck of a lot easier.

Person counting Euro banknotes over financial charts
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For all the liberal arts majors out there, if you have a practical math tip, float it to us in the comments below and your tip could be used in an upcoming BuzzFeed Community post. Thanks for helping all of the right brains out!

Cady Heron in 'Mean Girls' stating "The limit does not exist" during a math competition
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