combining functions question 4

**math123456** · January 10th 2009, 06:35 PM

Increasing x by y% gives 12. Decreasing x by y% gives 8. Deteremine the value of x.

**Soroban** · January 10th 2009, 06:57 PM

Hello, math123456!

I don't see how this relates to "combining functions."
It is straight algebra . . .

Increasing $x$ by $y$ % gives 12.
Decreasing $x$ by $y$ % gives 8.
Deteremine the value of $x.$

We have: . $\begin{array}{cccccccc}x(1+y) &=& 12 & \Longrightarrow & x + xy &=& 12 & {\color{blue}[1]} \\<br /> x(1-y) &=& 8 & \Longrightarrow & x - xy &=& 8 & {\color{blue}[2]} \end{array}$

Add [1] and [2]: . $x \:=\:20 \quad\Rightarrow\quad\boxed{x \:=\:10}$

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