Multicols: how to modify the width for each column

I am writing a poster and I am using the multicols environment in order to divide each section. The poster is organized in horizontal sections and each one is organized in two or more columns. For only one horizontal section I would like to have three columns, the first two of which should be smaller (width) than the third one. For this section, I am currently using the following:

\fbox{

\parbox{1.014\boxwidth}{
\setlength{\fboxsep}{0.005\textwidth}
\setlength{\fboxrule}{0.00125\textwidth}
\setlength{\columnwidth}{1.02\linewidth}

\newpart{Results \& Discussion}

\vbox to 0.375\textheight {%
\raggedcolumns
\setlength{\columnseprule}{0.pt}

\begin{multicols}{3}

\begin{center}
\end{center}

{Some text}

\begin{center}
\end{center}

{Some text}

\begin{center}