I am drawing two very simple curves with TikZ. Here's my code:
\documentclass[border=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,arrows.meta}
\begin{document}
\begin{tikzpicture}[font=\normalsize]
\draw [very thick,-Triangle] (-0.02,0) -- (10,0); % X-axis
\draw [very thick,-Triangle] (0,0) -- (0,5); % Y-axis
\draw [very thick] (0,0) to[out=25,in=-230] (2,3) to[out=-50,in=180] (4,0);
\draw [very thick] (2,0) to[out=0,in=-180] (4,1.5) to[out=0,in=90] (5,0);
\end{tikzpicture}
\end{document}
What's the simplest way to fill in the area below the curves as shown in my mockup?


\begin{scope} \clip <left-hand page>; \fill[purple] <right-hand path>; \end{scope}. Also, remember to do all of the filling before drawing. – Andrew Stacey Aug 17 '21 at 08:33