Hey everybody! Gather round; I just discovered this incredible ancient way for multiplying! It& #39;s so simple; here& #39;s what you do: Say you want 3x4. So you make 3 horizontal lines, and 4 vertical lines, and count the intersections! I can& #39;t believe nobody ever showed me this!(cont& #39;d)
2/ Actually I& #39;m not just trolling, I do have a point. People keep getting excited by "new algorithms" like this because adults, while fully capable of executing the "standard" algorithm, actually have zero understanding of *why* it works. Let& #39;s look at it together:
3/ Say you& #39;re multiplying 123x45. So you do 5x3 = 15, write the 5 but carry the 1 (above the 2). Then 5x2=10 but remember to add the 1 (add? I thought we were multiplying?), so really 11; write the 1 and carry another 1. Finally, 5x1+1=6. So our first row is 615. What the hell?
Now imagine teaching this to a child learning it for the first time. It makes no sense (and the grownup doesn& #39;t know why either, but they& #39;ve been dutifully trained on it).

Then somebody comes along with a "Japanese" method, and we all get excited that we "finally understand".
5/ So what *is* going on in the standard algorithm?

Remember: multiplication is all about rectangles! When you ask for 123x45, you want the area of a 123x45 rectangle. Since 123=100+20+3, you really want (100+20+3)x(40+5). Maybe you were taught something called "distribution"
6/ but that was a long time ago. Just draw a picture, and all becomes obvious! Starting in the top right and going across, the little corner is 5x3=15, then 5x20=100, then 5x100=500; those three add up to 615. *That* is exactly what that first row means in the standard algorithm.
7/ The most "natural" way to track this is to just write all the products out and add (as shown). This is actually what I teach my own kids, not the standard.

Now, this gets a little tiresome, with all those zeros, so the standard algorithm compresses them to save space+time.
8/ That compression was important when "calculator" meant a human; these days nobody does 8917x124 by hand. (That doesn& #39;t mean it& #39;s not important for people to understand what multiplication means or how to do it efficiently!)

Anyway, if you want to "test" some newfangled method
9/ just give it some slightly larger numbers than the "cute", carefully chosen example they show you. I don& #39;t think anybody would be retweeting the "Japanese method" if it was illustrated on 78x93...

End of rant.
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