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I'm really embarrassed to ask this - my apologies.

In a piece of software I'm writing, I am using the following:

$Y = X+\frac{X}{10}N$

That's all fine - but how do I calculate X when I know Y and N?

I know it's really basic, but for some reason I get stuck half-way through moving the equation around.

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Please clarify, is it $\frac{X}{10N}$ or $\frac{X}{10}N$ ? (Parentheses are hella important!) –  J. M. Nov 23 '10 at 11:14
    
SOrry, it is Y = X + ((X/10)*N) –  palmaceous Nov 23 '10 at 11:18
    
Note then that $Y=X(1+\frac{N}{10})$; thus, $X=\frac{Y}{1+\frac{N}{10}}$ ... –  J. M. Nov 23 '10 at 11:27
    
Spot on, that works perfectly. –  palmaceous Nov 23 '10 at 11:35
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@Arturo, done now. –  J. M. Nov 23 '10 at 15:19
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1 Answer

If $Y=X+\frac{X}{10}N=X\left(1+\frac{N}{10}\right)$, then $X=\frac{Y}{1+\frac{N}{10}}$ .

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