The "fascinating little hack" involves flipping the numbers around to make things easier - and is described as "life changing" by people on Twitter.
For example, if you need to work out 18% of 50, swap them and go for the easier option of 50% of 18 instead. The answer for both is nine.
Another example is 4% of 25. Flip it round to work out 25% of 4 - and the answer to both is one.
Whaaaat?! Why didn't they teach us this in 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.
— Ben Stephens (@stephens_ben) March 3, 2019
Hello new party trick! We feel like Rainman when we do this!