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.
Mind blown. Take your shoe size. Times by 5. Add 50. Times by 20. Add 1015. Subtract yr you were born. Answer = your shoe size and your age.— Lucy Tobin (@lucytobin) January 15, 2016
Others reacted in a similar fashion.
@lucytobin WHAT how did that just happen— Kate Leaver (@kateileaver) January 15, 2016
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?