%% 
%%  An UIT Edition example
%% 
%%  Example 09-18-2 on page 194.
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{30}
\renewcommand\theequation{9.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath,graphicx}
\newcommand*\Sum[1][1]{\ensuremath\mathop{\scalebox{#1}{$\displaystyle\sum$}}}
\StopShownPreambleCommands
\begin{document}
\begin{align}
 \Sum_{i=n}^ma_i\cdot\sum_{j=l}^kb_j &= \Sum[1.2]_{i=n}^m\Sum_{j=l}^ka_ib_j
\end{align}
\end{document}