Just multiplied a 10 digit number by 12 in my head!! Blog Discussion

Former_MSE_Andrea

This is a chat forum discussion on Martin's 'Just multiplied a 10 digit number by 12 in my head!!!!!' blog which you can read here.

quoia

He's obviously had a bout of MENTAL Arithmatic..

nelly_2

I got one of them memory books once and its sort of usefull I managed to memorise the serie A in order for that particular week and you can apply it to anything, but and as daft as it sounds you dont remember to do it when you put the car keys down and thats why you cant remember where they are.

This numbers one sounds more usefull though I hardly ever have to work things out anyway.

Ticklemouse

Hell - I still have to think about 8 x 7!! :rotfl:

bob_regis

Play.com have it for £5.99 go through quidco and get some cashback.

http://www.play.com/play247.asp?source=327&page=title&Cur=257&r=BOOK&title=429184&tduid=2a20b8f722f3cec5aa96ed02e3a4c88a

bigandy_3

I was intrigued by the ability to learn a new skill and party trick (imagine: "I bet you £20 I can multiply a ten digit number by 12 in my head!"), so I found the following page which gives you an idea of the technique;

http://mathforum.org/dr.math/faq/faq.trachten.html

But my word! It's not exactly straightforward !

MSE_Martin

Dont worry the book includes exercises and makes it much easier to do. And let me clarify what 'multiply a 10 figure number by 12 in my head' means.

While i can (sometimes) do three figures by two figures now ie 248 x 38.

As for the rocess of a 10 figure by 12 in my head, you effectively do it one digit at a time (in reverse!) i couldn't remember it.

Thus if someone said multiply 2285643939 by 12, I couldn't reel off the number. However I could write it down without any workings

martin

CIS

Theres a good intro to the system here

http://en.wikipedia.org/wiki/Trachtenberg_system

dchurch24

That's bizzarre! My dad had this book on his bookshelf when I was roughly 16 (he'd bought it a train station while waiting for a train one day many years ago), and I'd found it and read a little bit of it and found it quite interesting.

A few years later (about 15 years actually), I was telling a friend about it and I couldn't find the book anywhere, so we both bought a copy on Amazon and amazed each other with ridiculous sums over the phone.

Indeed, this method of maths is the ONLY method they teach in Switzerland - my partners family all live in Switzerland and so I asked them to verfy the claim in the book and it's true - apparently!

Very good read - even the intro which is a brief history of Tractenburgs life.

En_Kay

You should try Rapid Math Tricks and Tips by Edward Julius. It contains various tricks to enable mental multiplication/division etc.. Some are very, very simple.

sneekymum

Read the reviews of this similar (but clearly inferior) book...

(start at the bottom)