%% 
%%  An UIT Edition example
%% 
%%  Example 10-09-2 on page 216.
%% 
%%  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}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{24}
\renewcommand\theequation{10.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath,array}
\AtBeginDocument{\setlength\tabcolsep{0pt}
\renewcommand\arraystretch{0}
\setlength\abovedisplayskip{0pt}
\setlength\abovedisplayshortskip{0pt}
\setlength\belowdisplayskip{0pt}
\setlength\belowdisplayshortskip{0pt}}
\newcommand*{\diff}{\mathop{}\!\mathrm{d}}
\StopShownPreambleCommands
\begin{document}
\begin{subequations}
\begin{tabular}{@{}*{2}{m{0.5\linewidth}}@{}}
\begin{align} \oint E \mathrm{d}s=0 \end{align}
  & \begin{align} \nabla\times B=0 \label{sub:foo}\end{align}\\
\begin{align} a =\frac{c}{d} \end{align}
  & \begin{align} b = 1 \end{align}          \\
\begin{align} c =1 \label{sub:baz}\end{align}
  & \begin{align} \int 2x\diff x = x^2+C \end{align}
\end{tabular}\par
All subequations can be referenced in the usual way. For example,
equations~\eqref{sub:foo} and~\eqref{sub:baz} are given correctly with their
letters. The label has to be set correctly of course.
\end{subequations}
\end{document}