Splitting fraction numerator into several lines

Question

I need to write a fraction for which I can break the numerator into several (not just two) lines. I tried several solutions and none have works. On Overleaf, most just stop the document from compiling. These are my latest attempts:

\begin{align*}
    \frac{\begin{split}{2102 – 400 + \\ 1873 – 400 + \\ 1949+ \\ 1800 – 400 + \\ 1314 + 400 + \\ 1473 + \\ 1901 + 400}\end{split}}{7}
\end{align*}

and (this was a first split; I would have used  \splitfrac again if that had worked)

\begin{align*}
    \frac{\splitfrac{2102 – 400 +}{1873 – 400 + \\ 1949+ \\ 1800 – 400 + \\ 1314 + 400 + \\ 1473 + \\ 1901 + 400}}{7}
\end{align*}

Even better (but not indispensable), I'd like to annotate each line of the numerator. Is that possible? To indicate what each line represents.

NOTE: I ended up doing this by putting matrix in the numerator. That just solved everything for me in a very easy way.

Answer 1

I'm not sure I understood your comments fully, but \splitfrac instructions can certainly be nested. Each instance of \splitfrac creates a linebreak; three nested \splitfrac directives, for instance, result in four lines overall.

The \mathstrut directives serve to insert a bit of extra vertical whitespace.

\documentclass{article}
\usepackage{mathtools} % for \splitfrac macro
\begin{document}
\[
 \frac{\splitfrac{2102 - 400 + 1873\mathstrut}{
       \splitfrac{{} - 400 + 1949 + 1800\mathstrut}{
       \splitfrac{{} - 400 + 1314 + 400\mathstrut}{ 
                   + 1473 + 1901 + 400\mathstrut}}}}{7}
\]
\end{document}