Multiplication Using Lines

Do you have troubles with multiplication? Below the video is a demonstration of an easy way to multiply large numbers together. How long has this method been known? Why were we never taught this when we were kids?

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Hmm, interesting. First thing I tried was a 3-digit x a 2-digit number; took a bit to figure out how to do the intersection groupings for a mismatch like that, but it does indeed work.

Wow. Clever trick.

By G Barnett (not verified) on 30 Jan 2007 #permalink

That's snazzy, but there's an easy answer as to why this is more of just something fun rather than something that should be taught in school.

Try to do:99*88 (for example). I can't draw that many straight lines!

That is fracking cool. I would have loved that when I was a kid.

By writerdddd (not verified) on 30 Jan 2007 #permalink

Even more to the point:

Try 101*101

If you draw a line that no one can see, does it really exist?

Interesting. You'd have to use stub lines/points to represent the zeroes, but it's doable. I just worked out 101 x 101 & for added confirmation, 2301 x 101. The trick then becomes knowing where to draw those grouping curves.

Actually, one could conceivably use this format for representing numbers in a handwritten cipher and really mess with folks. Say, do the usual 1-26 for representing A-Z, then break words into letter pairs, and then write it out as line-multiples of the pairs. I suppose you could also pre-encode as ROT-13 to really obfuscate things.

That might be something for me to do to my D&D group the next time I'm DM....

By G Barnett (not verified) on 30 Jan 2007 #permalink

Re: 101 * 101, Just draw dashed lines for the zeros and count the intersection of a dashed line as a zero. It works, 10201.

By TonDunlap (not verified) on 30 Jan 2007 #permalink

I think a proof of this would be really nice.
I'm working on one now.
I'll keep you posted on whether I get one or a counter example.

Well, yes, that makes sense. You're just doing the exact same thing you would when you multiply, but visually. Then again, some kids are visual learners, and this might help them understand multiplication - it's more fun than looking at numbers.

Just get a calculator and get over it. There's no way I'm making posters out of my math problems, and counting dots.

What's to prove? All it does is a 'dot' style of multiplication as opposed to writing numbers and having to do the math in your head first.

By making it a diagonal on its corner, you quickly see how many digits the end result should have (in the second example, it was 5 because there were 5 diagonals) In effect, you're not doing anything that 'long' multiplication never taught you, you're just doing it by counting dots laid out in a certain way rather than writing down the Arabic numerals.

This looks like it could be LOADS of fun, though!

Does any1 no wat this is called...i cant find any ifo n it....and how long its been around....email me info at longy3_spunk@hotmail.com and provide any website pls