\documentclass{minimal}
\let\mypercent\%
\usepackage{amsmath}
\usepackage{xepersian}
\settextfont{Yas}
\setdigitfont{Yas}
\begin{document}
20\%

$30\%$

$$30\%$$

$$30\mypercent$$

$30\text{\lr{٪}}$

%$40\text{\lr{%}}$


\end{document}