I came across this bizarre yet sophisticated system of multiplication used in Ethiopia before the age of calculators and computers.
In order to multiply any two numbers, all you need to know is how to halve a number and how to double it. Don’t believe it? Check out the video below:
Essentially, this ancient system breaks the multiplication into powers of 2 (i.e. base 2 arithmetic) – which is exactly the system that computers and calculators use today!
While we’re at it, here’s a fine trick to find out the multiples of 9:
[T]o find the product of 9 times n, hold your hands out in front of you and fold down your nth finger from the left to separate the tens and the ones. For example, to find 9×4, you would hold down your 4th finger from the left […]. The bent finger separates the tens and ones digits, so the configuration of 3 fingers (folded finger) 6 fingers gives the answer of 36.
[Hat Tip: 360]