\documentclass{article}
\usepackage[UTF8]{ctex}   % Handles Chinese text properly
\usepackage{amsmath}      % Enables \frac and \approx

\begin{document}

\[
\mbox{理論遠期匯率} = 31 \times \frac{1.015}{1.05} \approx 29.95
\]

\end{document}