Japanese Multiplication, using lines.

[sl8]

Japanese Multiplication Method

[unblock]

1. clever trick!

[Bernardo de La Paz]

2. Nice. ABC x XYZ

ABC x XYZ =
A00 x X00 + A00 x Y00 + A00 x Z
          + B0 x X00 + B00 x Y0 + B00 x Z
          + C x X00 + C x Y0 + C x Z

[eppur_se_muova]

3. A variation on the "gelosia" or "lattice" method --

Can be done with numerals instead of lines -- much better for larger numbers, since you don't have to count anything.

http://www.tandfonline.com/doi/abs/10.1080/17498430701581045?journalCode=tbsh20

[sl8]

5. Excellent, thanks for posting that.

I' d never heard of the "gelosia" or "lattice" method before. Very cool.

Also, Ms. Boag's anecdote about how she came across it in use was interesting.

Now, off to watch some videos about Napier's Rods (Napier's Bones?). I had never heard of that before, either.

[docgee]

4. Meh. Doing math in your head by imagining lines probably doesn't work very well.

[gratuitous]

6. Reminds me of an Asimov short story

In the near future (the story was written in the 1970s or 1980s), everyone is totally dependent on computers to carry out simple math problems. Some flunky in a cube is punching numbers into his computer for eight hours a day every day and noting the results. His mind starts wandering, and he pulls out a pencil and paper and rediscovers a system for multiplying numbers. He checks his work against the computer and is delighted to find out he's right. He starts having a little fun with it, then shows his boss, who is amazed that the correct answer can be had without the computer.

Figuring products becomes a parlor trick, then a fad, and finally is reserved for the idle wealthy, who figure products and sums while po' folk are dependent on their computers for their math needs. It was a clever little story showing how fortune's wheel sometimes turns.