Scalable If/Then Structure

An ideal usecase for luatex:

\documentclass[margin=1mm, varwidth=true]{standalone}
\usepackage{luacode}

\begin{luacode}
  userdata = userdata or {}

  local questions = {
      "1 + 2 = 3" ,
      "2 + 1 = 3" ,
      "3 = 2 + 1" ,
      "3 = 1 + 2" ,
    }

  function userdata.fact()
    local A = math.random(#questions)
    tex.print(questions[A])
  end
\end{luacode}

\newcommand\Fact{\luadirect{userdata.fact()}}

\begin{document}

\begin{itemize}
  \item $\Fact$ 
  \item $\Fact$ 
  \item $\Fact$ 
  \item $\Fact$ 
  \item $\Fact$
\end{itemize}

\end{document}

which gives

If you have 100 different cases, then your code logic is wrong at some point. But for not too many cases you can do \ifcase

\documentclass{article}
\usepackage{pgfmath}

\pgfmathsetseed{\number\pdfrandomseed}
\pgfmathtruncatemacro{\A}{random(1,4)}

\begin{document}

\ifcase\A\relax%
  \or 1+2=3% Because \A starts from 1
  \or 2+1=3%
  \or 3=2+1%
  \or 3=1+2%
\fi

\end{document}

I think it's easy to define essentially an array of options so you can define or redefine them as needed without having to define them all together in a nested structure.

\documentclass{article}

\usepackage{pgffor}

\usepackage{ifthen}

\pagestyle{empty}
\setlength{\parindent}{0pt}

% THE FOUR EQUATIONS
% 1.   1+2=3
% 2.   2+1=3
% 3.   3=2+1 
% 4.   3=1+2

\def\defchoice#1#2{\expandafter\def\csname X-#1\endcsname{#2}}
\defchoice{1}{$1+2=3$}
\defchoice{2}{$2+1=3$}
\defchoice{3}{$3=2+1$}
\defchoice{4}{$3=1+2$}

\pgfmathsetseed{\number\pdfrandomseed}

\newcommand{\InitVariables}
{\pgfmathsetmacro{\A}{random(1,4)}} 

\newcommand*{\onefact}
{%%%%%%%%%% dont forget % at end of line
 \InitVariables
  \csname X-\A\endcsname}


\newcommand{\myequations}[1]
{%
 \foreach \x in {1,...,#1}
  {\onefact\par}% don't end a paragraph with \\
}

\begin{document}

\myequations{10} 

\end{document}