Maths wizardry with lines
2010-May-02, Sunday 01:05![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
You thought you knew maths? YouTube - Alex Bellos demonstrates a very cool, and strange way to multiply:
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?
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?
no subject
Date: 2010-May-02, Sunday 00:31 (UTC)The only thing that you're doing differently is that for each individual pair of digits that you multiply, instead of just doing it in your head, you're drawing lines and counting their intersections. That's fine when you're doing 2*3 and want to draw 2 lines crossing 3 lines and count up that there are 6 intersections, but it really comes unstuck when you need to multiply 7 by 9 when even drawing all the lines becomes difficult, let alone counting up the 63 points.
There's a similar method where you construct a grid, multiply the individual digits and then add up the diagonals, which is essentially the same as the method in the video, but with standard multiplication (either by memory or by repeated addition) instead of lines. I think there is something to be said for teaching that method in schools. It's a little unwieldy, certainly, but it's always good to have different approaches to be able to use since different ways of looking a things will click for different people.
no subject
Date: 2010-May-02, Sunday 11:52 (UTC)I've never liked one-size-fits-all methods, mostly they work for me but when they don't I get all confused.
Juggling intersections
Date: 2010-May-02, Sunday 12:30 (UTC)no subject
Date: 2010-May-03, Monday 22:32 (UTC)http://i800.photobucket.com/albums/yy285/poifaerie/GridMultiplication.jpg
~ poifaerie @ LJ
no subject
Date: 2010-May-02, Sunday 10:40 (UTC)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.
no subject
Date: 2010-May-03, Monday 22:08 (UTC)A nice trick if you can do it, though!
no subject
Date: 2010-May-02, Sunday 13:02 (UTC)The problem is that this technique is very bad when dealing with large individual numerals. I believe there were other multiplication techniques available though...
no subject
Date: 2010-May-02, Sunday 13:16 (UTC)