This is incredible.
Cast your mind back to maths class at school. Chances are you found the subject a little tedious.
But numbers can be exciting. At least they can when appearing to conjure some sort of mysterious witchcraft.
This 'maths trick' has been around a little while, but cropped up on Twitter on Friday and dumbfounded some people.
The formula works out your shoe size and age in six simple steps - to begin, the method requires only your shoe size, and then guides you through the process to magic up the your age.
It worked for us, but there's a distinct caveat - the whole thing only works if you've not yet had your birthday. But it's early 2016, so it should work for most of you.
Others reacted in a similar fashion.
If you want a relatively simple solution and explanation, there's one here. It's algebra - there's method to the mathsness.
More: Can you pass GCSE maths?