Math Is Fun Forum

koconnor

Member

Registered: 2008-02-09

Posts: 2

Multiply by 12 Shortcut

So how does the 12’s shortcut work?

Let’s take a look.
12 X 7

the first thing is to always multiply the 1 of the twelve by the number we are multiplying
by, in this case 7. So 1 X 7 = 7.

Multiply this 7 by 10 giving 70. (Why? We are working with BASES here. Bases are the
fundamentals to easy calculations for all multiplication tables. To find out more check out
our Vedic Maths ebook at http://www.memorymentor.com/big_brain.htm)

Now multiply the 7 by the 2 of twelve giving 14. Add this to 70 giving 84.

Therefore 7 X 12 = 84

Let’s try another:

17 X 12

Remember, multiply the 17 by the 1 in 12 and multiply by 10

(Just add a zero to the end):

1 X 17 = 17, multiplied by 10 giving 170.

Multiply 17 by 2 giving 34.

Add 34 to 170 giving 204.

So 17 X 12 = 204

lets go one more

24 X 12

Multiply 24 X 1 = 24. Multiply by 10 giving 240.

Multiply 24 by 2 = 48. Add to 240 giving us 288

24 X 12 = 288 (these are Seriously Simple Sums to do aren’t they?!)

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Kurre

Member

Registered: 2006-07-18

Posts: 280

Re: Multiply by 12 Shortcut

But that is just that the normal way you proceed when multiplying any numbers with each other...where is the "shortcut"??

koconnor

Member

Registered: 2008-02-09

Posts: 2

Re: Multiply by 12 Shortcut

I understand where you are coming from with the normal way.

When I was growing up I was taught to learn the 12 times tables off by heart... 1 X 12 is 12, 2 X 12 is 24 etc...

The way I have it laid out was something that had come about by thinking about it... If that's how it is learned in other countries then great!

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JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Multiply by 12 Shortcut

The method isn’t really a shortcut. However, it shows that you understand how multiplication of numbers of two or more digits work.

So: if you are also having problems with your times tables for 13, 14, 15 … just use the same method. For example, to multiply 7 × 17:

(i) add a “0” to the “7” → 70
(ii) multiply 7×7 → 49
(iii) and add the two numbers → 70 + 49 = 119

Hence 7 × 17 = 119.

It is always great to know not just that something works but also how it actually works.