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#1 2013-02-02 05:16:57

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Proportion

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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#2 2013-02-02 06:26:06

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,199

Re: Proportion

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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#3 2013-02-02 06:30:18

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Proportion

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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#4 2013-02-02 06:34:45

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,199

Re: Proportion

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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#5 2013-02-02 07:28:41

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Proportion

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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#6 2013-02-02 07:32:09

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,199

Re: Proportion

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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