This is amazing! Russian Multiplication: A Different Way to Multiply. Video, 7 minutes.
In Russian multiplication you can multiply any two numbers together through simple addition and doubling & halving numbers.

@Burk This guy is really good at explaining things - I edited an article on the history of multiplication once and the author could’ve used pointers from him. Also, you haven't lived until you've tried Babylonian multiplication (bonus point if you typeset it in LaTeX!)

@seishonagon @burk It's a very clever method, but I was thinking maybe the style I learned at school is easier to do entirely in one's head (9 times 3 is 27, carry the 2; 9x1 is 9, add the 2 = 117).

@Burk Definitely, but it’s a product of circumstances. Our method works with educated people who use a decimal writing system. Try doing it in hieroglyphics, or without memorizing your times tables ...

@bix Haha! Metoo! Although I use addition and subtraction in my head, when I don’t have a calculator nearby.