\documentclass[a4paper]{article}
\usepackage[landscape,margin=1cm]{geometry}
\usepackage{times}
\usepackage{anyfontsize}
\usepackage{pict2e}
\usepackage{color}
\newenvironment{puzzle}{\noindent\mbox{}\vfill}{\newpage}
\newcommand\puzzles{
\fontsize{36}{42}\selectfont
\setlength{\unitlength}{2.1em}
\input{mixed}
%
\setlength{\unitlength}{2.5em}
\input{multiplication}
}
\begin{document}
\bf
\newcommand\hidden[1]{}
\puzzles{}
\renewcommand\hidden[1]{\textcolor[gray]{0.5}{#1}}
\puzzles{}
\end{document}