This method is not Japanese as far as I know. A generalization of this method was used by Babbage used it to build his differential engine:http://www.computerhistory.org/babbage/howitworks/
or you get a calculator and be done in 2 seconds...
I would be quite impressed if you managed to get a calculator AND type in the equation within 2 seconds.
are you trying to tell me you don't have a necklace calculator on at all times?
now try that with a simple multiplication like: 8 x 9 lol than you need to count 56 crossing lines (cross points)but still a cool way to multiply!
Mind = Blown
easy with small digit like 1 2 3, but with 7 8 9 will be a pain to count and draw
Is it sad I can do this type of math in my head without counting line intersections?
I don't think I've ever seen anyone in Japan using this method.
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