We can set up a proportion. The ratio of its length to width is 8 to 5. The longer side of the rectangle is 20 ft, or the length. So we have:
[tex]\sf\dfrac{8}{5}=\dfrac{20}{x}[/tex]
Cross multiply:
[tex]\sf (5)(20)=(8)(x)[/tex]
[tex]\sf 100=8x[/tex]
Divide 8 to both sides:
[tex]\boxed{\sf x=12.5}[/tex]
So the length of its shorter side(width) is 12.5 feet.
