Roman numbering in table of contents using report

Question

Using the MWE below, I want the chapters declaration, preface and abstract to be given a roman number in the table of contents and the rest of the chapters arabic numbers, using the report class. The table of contents, however, seems to ignore the chapters I want to be roman numbered. It is possible if I use memoir rather than report, but than the subsections are not shown in the table of contents.

\documentclass[a4paper,12pt]{report}
\begin{document}
\tableofcontents
\chapter*{Declaration}
\chapter*{Preface}
\chapter*{Abstract}
\chapter{Introduction}
\chapter{Topics in Claims Reserving}
\section{section 1}
\subsection{section2}
\chapter{Conclusion}
\end{document}

Answer 1

You can use book and then it has \frontmatter for the very same purpose. (Same is possible with memoir, you can always change the tocdepth)

\documentclass[a4paper,12pt]{book}
\begin{document}
\frontmatter
\tableofcontents
\chapter{Declaration}
\chapter{Preface}
\chapter{Abstract}
\mainmatter
\chapter{Introduction}
\chapter{Topics in Claims Reserving}
\section{section 1}
\subsection{section2}
\chapter{Conclusion}
\end{document}

If you want report, you have to do this:

\documentclass[a4paper,12pt]{report}
\begin{document}
\pagenumbering{roman}
\tableofcontents
\chapter*{Declaration}
\addcontentsline{toc}{chapter}{Declaration}
\chapter*{Preface}
\addcontentsline{toc}{chapter}{Preface}
\chapter*{Abstract}
\addcontentsline{toc}{chapter}{Abstract}
\cleardoublepage
\pagenumbering{arabic}
\chapter{Introduction}
\chapter{Topics in Claims Reserving}
\section{section 1}
\subsection{section2}
\chapter{Conclusion}
\end{document}

For all the odd things that may happen (and I don't understand properly)

\documentclass[a4paper,12pt]{report}
\usepackage{tocloft}
\setlength{\cftchapnumwidth}{3em}
\cftsetindents{section}{3em}{1.5em}
\cftsetindents{subsection}{4.5em}{2.5em}
\begin{document}
\renewcommand{\thechapter}{\Roman{chapter}}
\tableofcontents
\chapter{Declaration}
\chapter{Preface}
\chapter{Abstract}
\cleardoublepage
\setcounter{chapter}{1}
\renewcommand{\thechapter}{\arabic{chapter}}
\pagenumbering{arabic}
\chapter{Introduction}
\chapter{Topics in Claims Reserving}
\section{section 1}
\subsection{section2}
\chapter{Conclusion}
\end{document}