Japanese multiplication technique - GIF

[mklotz]

Looks nice. Try 76x47...

Or 99 x 99.

Gonna be drawing a lot of lines and counting a lot of intersections. I fail to see any advantages to their system.

99 x 99 = (100 -1) x (100 -1) = 100 x 100 - 200 + 1 = 9800 + 1 = 9801

would seem a lot simpler - can even do that one in your head.

76 x 47 = (80 - 4) x (50 - 3) = 4000 - 240 - 200 + 12 = 3560 +12 = 3572

Ok, a bit more difficult but still simpler than drawing all those lines.

[jarekp]

Or having paper, "western" oldschool method:


76
47
--------
532
304
-------
3572

At least no limits of digits.

Btw
Have you imagined that Copernicus was able to do quite complicated calculations?
Try to do above using roman numbers (he did not know other)....
J.

[mklotz]

...
Have you imagined that Copernicus was able to do quite complicated calculations?
Try to do above using roman numbers (he did not know other)....

The awkwardness of computation using Roman numerals probably accounts for the Romans' use of the abacus.

The Roman abacus was similar to modern ones but had some additional columns at the right...



The Wikipedia article provides a full description of the device and its use...

https://en.wikipedia.org/wiki/Roman_abacus