# This incredibly simple math trick is blowing people’s minds on Twitter

Humans

It’s not always easy to work out percentages in your head, but a simple maths trick being shared on Twitter can make it incredibly easy to perform difficult or unwieldy mathematical calculations on the spot.

Described as a “fascinating little life hack” by UK-based copywriter Ben Stephens, the trick involves doing a simple number swap to figure out your answer. It’s not a new technique, but the huge reaction online shows lots of people never knew the workaround existed.

As Stephens explains, if you ever have to calculate a difficult percentage on the spot without pen and paper or a calculator, you can use a simple shortcut – flip the numbers around.

“So, for example, if you needed to work out 4% of 75 in your head, just flip it and and do 75% of 4, which is easier,” Stephens tweeted.

Indeed, if you swap the numbers and calculate 75 percent of 4, you get 3 – and 3 is the same answer when you calculate 4 percent of 75. (In case it doesn’t click straight away, 75 percent is three quarters, so in this case it becomes a simple division problem.)

Another example: “18% of 50 feels hard to calculate,” Stephens wrote. “But 50% of 18 is a doddle, right?”

This basic principle – simply stated as x% of y = y% of x – is probably well known to millions of people across the world.

But as the tweetstorm generated by Stephens’ original comment shows, it’s a mind-blowing discovery for many who were never made aware of this simple substitution, with one user saying the revelation “got me excited about math for the first time in decades”: