\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}