How Japanese Kids Learn To Multiply • Hacker News Board

Re: How Japanese Kids Learn To Multiply

#31

Post by Aardwolf » Mon, Jan 14, 2013, 4:25 PM UTC

acomjean wrote: post #26

I see the video, but how does this work? on unix/linux I just use bc -l

bc is a pretty misleading calculator, without specifying rounding it thinks 2^(40/1.5) is 67108864.

It's not even close.

If you trust your finances to that, you could get in trouble.

Re: How Japanese Kids Learn To Multiply

#32

Post by Aardwolf » Mon, Jan 14, 2013, 4:31 PM UTC

est wrote: post #13

nice trick for numbers with each digit smaller than 5

I think only smaller than 4...

I wonder if this works in binary :D

Re: How Japanese Kids Learn To Multiply

#33

Post by antiterra » Mon, Jan 14, 2013, 4:36 PM UTC

I'm partial to vihart's perspective on this at http://www.youtube.com/watch?v=a-e8fzqv3CE It's moderately interesting, but ultimately just a way of doing the exact same thing. Multiplication can be reduced entirely or partially to counting, that's worth understanding. And, if explained correctly, this can give insight into multiplying polynomials. Also, showing that counting the intersections of 8 lines crossing 9 lines is tedious may present times tables as convenient time savers rather than teacher inflicted torture.

Re: How Japanese Kids Learn To Multiply

#34

Post by ricardobeat » Mon, Jan 14, 2013, 4:44 PM UTC

Still quicker to do the math in your head:

    123 * 321

    321 * 100 = 32100
    321 * 20  =  6420
    321 * 3   =   963
                -----
                39483

You just need to know the times table and keep a little stack in your head :)

Re: How Japanese Kids Learn To Multiply

#35

Post by muloka » Mon, Jan 14, 2013, 4:48 PM UTC

What's more impressive is flash anzan. The ability to visualize an abacus and then with it do additions of large sums rapidly and accurately.

Re: How Japanese Kids Learn To Multiply

#36

Post by leddt » Mon, Jan 14, 2013, 4:51 PM UTC

Aardwolf wrote: post #30

It doesn't work for 25x25, so what's the point?

It does work for 25x25.

Re: How Japanese Kids Learn To Multiply

#37

Post by sean-duffy » Mon, Jan 14, 2013, 4:58 PM UTC

This is quite a nice mathematical trick, but nothing more. It may allow children to be able to perform large multiplication at a young age, but it is also setting them up to be confused later on by providing them with a method which abstracts from the actual arithmetic. What on earth is going to happen when they run into algebraic multiplication? I think it is much more useful to teach them to split up the parts of the numbers and multiply those, if they are too difficult to be multiplied mentally. For example instead of 11x22 do 10x22 + 20 + 2.

Re: How Japanese Kids Learn To Multiply

#38

Post by Aardwolf » Mon, Jan 14, 2013, 4:59 PM UTC

leddt wrote: post #36

Aardwolf wrote: post #30

It doesn't work for 25x25, so what's the point?

It does work for 25x25.

You're right, I see it now, it represents 400 + 20*10 + 25 which is indeed 625. They just avoided those cases in the article and only showed those where the number of crossing neatly formed the digits.

Re: How Japanese Kids Learn To Multiply

#39

Post by esalazar » Mon, Jan 14, 2013, 5:03 PM UTC

I think that it is important to note that without good instruction no method is "good". It is really really important for anybody learning anything to understand fundamentally what is going on. This is the problem with most people that have math phobia's (I don't believe there are people that are not good at math). They are taught to memorize their times tables with only a fleeting mention that this really a summation. On this weak foundation people add more concepts, and BOOM they are math phobic. The thing I do like about the "line method" is it is a very visual way to show children what is going on. The chunks, if you will, are literally the place of the digit.

Re: How Japanese Kids Learn To Multiply

#40

Post by ricardobeat » Mon, Jan 14, 2013, 5:06 PM UTC

gklitt wrote: post #5

cincinnatus wrote: post #2

This is cool but not a part of any standard curriculum in Japan despite the title.

Agreed. I went to Japanese elementary school (in college now, so within the last 15 years) and didn't learn this lines method ever. What I found greatest about the Japanese method of learning multiplication was actually the method for learning single-digit products. The Japanese use a system called "kuku" (translated, "9 by 9") which involves memorizing a rhythmic chant that goes through the entire multiplication tab…

Isn't that the same as seven times seven equals forty-nine? In portuguese, sete vezes sete igual a quarenta e nove. Japanese doesn't look especially lengthy.