\begin{tabular}{c|c}
	\multicolumn{1}{c|}{$x_i$} & c($x_i$) \\ \hline
	\multicolumn{1}{c|}{$x_1$} & 2        \\
	\multicolumn{1}{c|}{$x_2$} & 1        \\
	\multicolumn{1}{c|}{$x_3$} & 5        \\ \hline
	\multicolumn{2}{c}{总频次$=8$}         
\end{tabular}
