# Quickly Multiply Big Numbers The Japanese Way

Japanese kids learn to multiply with a completely different method than the one you probably used as a kid. The Japanese maths voodoo/magic is more of a visual technique that involves drawing lines and counting the intersections.

The video above illustrates the basic method behind these magic lines. You draw lines on the diagonal to represent the numbers of the first number to multiply, then cross those lines with the other number's lines. Add up the intersections for each area, and you have the correct total.

I don't know how or why this works. But it's a pretty amazing trick and might make you wonder why we don't teach maths the way Japanese teachers do. If you want to learn more, Magical Maths showcases another YouTube video with this amazing method.

Math Magic [YouTube via Magical Maths]

Viral Mathematics.. who would have thought it? :) This video and the method has been doing the rounds in a major way over the last week or so. :)

Well. I'm no expert and happy to be corrected if wrong, but here's my take.

When you multiply, you cross things, say 2x3 = 6 is the amount of intersections between 2 lines and 3 lines. This seems to be doing that for each decimal place, and carrying when necessary.

I've always used the "break it down" method.

21 x 13 = ???

Break apart 21 in to three easily digestible parts. 10 + 10 + 1 = 21

10 x 13 = 130
10 x 13 = 130
1 x 13 = 13

273.

There are quicker ways, that's just the most basic and easy to understand.

Last edited 16/01/13 10:04 am

That certainly sounds easier than drawing lines and counting intersections.

123 x 321

100 + 10 + 10 + 3 = 123

100 x 321 = 32100
10 x 321 = 3210
10 x 321 = 3210
3 x 321 = 963

39483

I really doubt the Japanese do it this way, it seems to only work for low numbers making this sorta redundant not to mention painfully slow.

Also I've never seen a maths test that disallowed calculators.

NSW school cert (year 10) didnt allow calculators when I did it.

Also, someone should try to work out 474839748396743743894738 x 83434343565444367 using this method. I would.... but I'm lazy.

3.9617942706263078569853757314904e+40

like I said, I'm too lazy to actually do this myself, so I'll just assume you're correct.

He's using wolfram alpha or Google no doubt. Successful troll is successful!

Try calc.exe

You definitely didn't copy and past '474839748396743743894738 x 83434343565444367' into google or anything.

I've shown this to a number of Japanese friends, and none of them have ever been taught that way. I showed another friend of mine who said that it was the Russian way of doing maths

I highly doubt that. I didn't see vodka anywhere in that video clip.
OHHHH NO HE DIDN'T DO CULTURAL STEREOTYPING? OH YES HE DID!