Maths wizardry with lines

[matgb]

You thought you knew maths? YouTube - Alex Bellos demonstrates a very cool, and strange way to multiply:

Click to view

How weird is that? ( Via)

Can't afford to buy the book, does anyone know more about the method, because if multiplying were that easy surely they'd be teaching it in schools, especially for the less numerically gifted?

Comments

[two_brains]

I like it a lot. Never seen it before, but very cool.

It's a lot like grid multiplication, but probably great for people who prefer images to symbols. Definitely a tool to remember.

The problem (as I see it) for children's use, particularly those who are perhaps less mathematically skilled, is that I can immagine kids getting very confused about place value, particularly when carrying in the second example.

I always get kids who arent good at multiplying to use the grid method as it turns a hard multiplication into a number of easy ones followed by an addition.

[poifaerie]

Not only working out how many places to "move" a decimal, I can imagine a fair few would have difficulty in working out which groups to add together- especially if ther have problems with spatial awareness.

A nice trick if you can do it, though!

[lokean]

Crosswise multiplication. It's a technique in Vedic Mathematics, which has a large number of 'shortcut' or 'trick' techniques in it.

The problem is that this technique is very bad when dealing with large individual numerals. I believe there were other multiplication techniques available though...

[dainul]

I was going to say something similar - imagine 19*91, you'd have to count up 81 crosses at one corner alone.