Q:

How do I calculate the length and width for a known area and ratio?

I have a rectangle with a known area and a known ratio of length/width. How do I calculate the length and width. 
Area: 1500 sq ft
Ratio: 241 / 625 = .386
How do I calculate the length and width in feet. 

A:

Let the length of the rectangle be $l $ and the width be $w$. We know the area of the rectangle is $A = lw \tag {1}$.
Now it is given that $\frac {l}{w} = \frac {241}{625} \Rightarrow l = \frac {241}{625}w \tag {2}$.
Now substituting $(2)$ in $(1)$, we have, $$A = \frac {241}{625}w^2 =1500$$ $$w = \sqrt {\frac {1500\times 625}{241}} = \frac {10\times 25\times \sqrt {15}}{\sqrt {241}} = \frac {250\sqrt {15}}{\sqrt {241}} $$
Now I leave it to you to find $l$ using $(2)$. Hope it helps. 

