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

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Former MSE
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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.
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## Replies

• Forumite
14.4K Posts
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He's obviously had a bout of MENTAL Arithmatic..
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‹(•¿•)› Those that understand binary and those that do not!

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• 17.9K Posts
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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.
• Forumite
5K Posts
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Hell - I still have to think about 8 x 7!! :rotfl:
• Forumite
99 Posts
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• Forumite
42 Posts
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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 !
if i had known then what i know now
• MoneySaving Expert
8.3K Posts
Forumite
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
Martin Lewis, Money Saving Expert.
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• Forumite
12.3K Posts
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Theres a good intro to the system here

http://en.wikipedia.org/wiki/Trachtenberg_system
I no longer work in Council Tax Recovery but instead work as a specialist Council Tax paralegal assisting landlords and Council Tax payers with council tax disputes and valuation tribunals. My views are my own reading of the law and you should always check with the local authority in question.
• Forumite
1.2K Posts
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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.
• Forumite
1 Post
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.
• Forumite
4.8K Posts
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Read the reviews of this similar (but clearly inferior) book...

(start at the bottom)
still raining
This discussion has been closed.
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