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## #1 2013-02-03 04:16:57

Al-Allo
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### 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

## #2 2013-02-03 05:26:06

bobbym
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### 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.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #3 2013-02-03 05:30:18

Al-Allo
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### Re: Proportion

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

## #4 2013-02-03 05:34:45

bobbym
Administrator

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### 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.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #5 2013-02-03 06:28:41

Al-Allo
Full Member

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### 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 (2013-02-03 06:30:14)

## #6 2013-02-03 06:32:09

bobbym
Administrator

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### Re: Proportion

Hi;

You are welcome.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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