%% 
%%  \protect \LaTeX  -Referenz, 1. Auf"|lage 2007
%% 
%%  Example 7-6-13 on page 117.
%% 
%%  Copyright (C) 2007 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.
%% 

\documentclass{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{201.7051pt}
\setlength\parindent{0pt}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{gather}
\boxed{i_{11}=0.25}\\
\boxed{i_{21}=\frac{1}{3}i_{11}}\nonumber \\
\boxed{i_{31}=0.33i_{22}}
\end{gather}
\end{document}