SANTTUcurriculum vitae
14 Mar 2019

Never Struggle Again Calculating Percentages in Your Head Using this Simple Yet Amazing Trick

We all sometimes struggle calculating simple percentages in our head, whether it is to find how much we could save on a discounted sale or in calculating simple percentage returns on any investment we are likely to make. Nevertheless, this trick from a self-confessed “maths wizard” Ben Stephens, might make it easier than we think.


Not everybody has a flair for maths

Stephens recently tweeted a mind-blowing math trick on how to calculate percentages in your head. His surprisingly simple solution has now gone viral and left a lot of people wondering why it wasn’t taught at school.

Fascinating little life hack, for doing percentages:

x% of y = y% of x

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.

Twitter. Ben Stephens (@stephens_ben) March 3,


So what’s the key formula? It’s simple: x% of y = y% of x. Stephens explains, So, as an example, if you are required to figure out 4% of 75 in your head, simply flip it and do 75% of 4, which is less complicated. If you haven’t already worked it out, the solution is 3, and therefore this straightforward trick can be applied to any set of numbers. 18% of 50 feels onerous to calculate. Nonetheless, 50% of 18 is easier, right? you got it, it is 9 indeed.

Like multiplication, percentages conform to the commutative principle, which says the order of the terms does not matter. (Just as 


, it is also true that 40% of 5 = 5% of 40).

So the secret here is flipping the numbers around :). So try it out for yourself and share it with others!!

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