\(\#1\ method:\\\\\dfrac{5x}{8x}=\dfrac{5}{8}=\dfrac{5}{8}\cdot100\%=\dfrac{500}{8}\%=\dfrac{125}{2}\%=\boxed{62.5\%}\)
\(\#2\ method:\\\\ \begin{array}{ccc}8x&-&100\%\\5x&-&p\%\end{array}\ \ \ |cross\ multiply\\\\8xp=100\cdot5x\ \ \ |divide\ both\ sides\ by\ "x"
eq0\\\\8p=500\ \ \ |divide\ both\ sides\ by\ 8\\\\\boxed{p=62.5\ (\%)}\)