% decimals template
\documentclass[border = 1mm]{standalone}
\usepackage{dcolumn}

% Define a decimal-aligned column type
\newcolumntype{d}[1]{D{.}{.}{#1}}

\begin{document}
    % decimals diagram template
\begin{tabular}{c d{1.2}}
     &3.43 \tabularnewline
    $+$&1.50 \tabularnewline
    \hline
     & \tabularnewline
    \hline
\end{tabular}

\end{document}