\begin {frame}
\frametitle{\textbf{$titulo$}}
\justifying
\begin{columns}
\begin{column}{.48\textwidth}
\color{red}\rule{\linewidth}{4pt}
\begin{exampleblock}{Respuesta para $\Q_\texttt{sum}$ con $t=\langle c_1, 2011\rangle$}
\begin{itemize}
\item ($c_1,2011,[124]$)
\item ($c_1,2011,[208]$)
\end{itemize}
\end{exampleblock}
\end{column}%
\hfill%
\begin{column}{.48\textwidth}
\color{blue}\rule{\linewidth}{4pt}
\begin{exampleblock}{Respuesta para $\Q_\texttt{sum}$ con $t=\langle c_1, 2011\rangle$}
\begin{itemize}
\item ($c_1,2011,[124]$)
\item ($c_1,2011,[208]$)
\end{itemize}
\end{exampleblock}
\end{column}%
\end{columns}
\end{frame}