\documentclass[leqno, 12pt]{article}
\usepackage[a4paper, portrait, margin=2cm]{geometry}
\usepackage{amsmath}
\usepackage{multicol}
\usepackage{siunitx}
\usepackage{fancyhdr}


\sisetup{output-decimal-marker={.}}


\def \HeadingQuestions {\section*{\Large Name: \underline{\hspace{8cm}} \hfill Date: \underline{\hspace{3cm}}} \vspace{-3mm}
{<<title>> of decimals: Questions} \vspace{1pt}\hrule}

% raise footer with page number
\fancypagestyle{myfancypagestyle}{
  \fancyhf{} % clear all header and footer fields
  \renewcommand{\headrulewidth}{0pt} % no rule under header
  \fancyfoot[R] {\thepage} % place page number at the bottom right
  \setlength{\footskip}{14.5pt} % raise page number
}
\pagestyle{myfancypagestyle}  % apply myfancypagestyle

%
\begin{document}
\HeadingQuestions
\vspace{-5mm}
\begin{multicols}{3}
<<diagrams>>
\end{multicols}
\end{document}