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

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

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: 90,682

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 agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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

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

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: 90,682

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 agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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

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

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: 90,682

Re: Proportion

Hi;

You are welcome.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

Offline

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