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**Proportion**

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 294

I just have a little problem :

X 8

_= _

7 9

If I would want to solve for X, I would multiply by 7 for each side. Leaving x=56

___

9

But what I did is x=56

__

63

Could somebody explain me why it's wrong ?

Thanks

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

When you multiply by 7 you cancel the 7 on the left but not the 9 on bottom right.

Correct thing to do is to cross multiply

9x = 56

x = 56 / 9

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 294

But I mean not canceling the 9 but multiplying it by 7, it's not a right thing to do ? Thanks

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

If you multiply by 7 you are going to get:

x = 56 / 9 which is the same thing.

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 294

bobbym wrote:

If you multiply by 7 you are going to get:

x = 56 / 9 which is the same thing.

ok, I understood. Thanks

*Last edited by Al-Allo (2013-02-02 07:30:14)*

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,776

Hi;

You are welcome.

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**Proportion**