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Proportion seems simple enough for me. Example is $4:x = 2:5,$ and the answer is $x = 10.$

My problem is how do I solve for proportions with $3$ ratios like $x:3:y = -2:3:-4$ ?

Do I write it like

$$\frac{\frac{x}{3}}{y} = \frac{\frac{-2}{3}}{-4} $$ ?

Jon
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Cary Bondoc
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2 Answers2

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Just like chained equalities, you can break it apart. $x:3:y=-2:3:-4$ becomes $x:3=-2:3$ and $3:y=3:-4$. Now solve them independently.

Ross Millikan
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    I'll add that you can also use a third proportion, that of $x:y=-2:-4$. Not that that's helpful in this particular case, but the point is that there are three proportions you can extract from such a triple. – Wildcard Jan 09 '17 at 10:10
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We have: $x:3:y=-2:3:-4$

$\Rightarrow x:3=-2:3$

$\Rightarrow \dfrac{x}{3}=-\dfrac{2}{3}$

$\Rightarrow x=-2$

and

$\Rightarrow 3:y=3:-4$

$\Rightarrow \dfrac{3}{y}=-\dfrac{3}{4}$

$\Rightarrow \dfrac{y}{3}=-\dfrac{4}{3}$

$\Rightarrow y=-4$

$\therefore x=-2,y=-4$

Tazwar
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