Anonymous 2257
In this code

\documentclass[12pt,a4paper]{book}
\usepackage{amsthm,amsfonts,amssymb,amsmath}
\newif\ifsolutions
\solutionstrue
\theoremstyle{definition}
\newtheorem{ex}{%
\hypertarget{sol:\theex}{}}[chapter]
\Newassociation{sol}{Soln}{ans}
\renewenvironment{Soln}[1]{\par\bigskip\noindent{\bfseries \hypertarget{ex:#1}{}%

\begin{document}
\chapter{Try}
\Opensolutionfile{ans}[ans1]
\begin{ex}
First exercise
\begin{sol}
First solution.
\end{sol}
\end{ex}
\clearpage
\begin{ex}
Second exercise
\begin{sol}
Second solution.
\end{sol}
\end{ex}
\clearpage

\Closesolutionfile{ans}
\ifsolutions
\section{Solutions}
\input{ans1}
\fi
\end{document}


How to color number of Exercises?

![image.png](/image?hash=0508ba22edb1ea472dc3742846420ff7cf0d7cd9b271077b7bb3c460f2347663)
samcarter
You could define a new theorem style:


\documentclass[12pt,a4paper]{book}
\usepackage{amsthm,amsfonts,amssymb,amsmath}
\newif\ifsolutions
\solutionstrue

\newtheoremstyle{foo}%
{}{}%
{}{}%
{\bfseries}{:}%
{ }%
{\thmname{#1}\thmnumber{ \textcolor{blue}{#2.}}\thmnote{ (#3)}}

\theoremstyle{foo}

\newtheorem{ex}{%
\hypertarget{sol:\theex}{}}[chapter]
\Newassociation{sol}{Soln}{ans}
\renewenvironment{Soln}[1]{\par\bigskip\noindent{\bfseries \hypertarget{ex:#1}{}%

\begin{document}
\chapter{Try}
\Opensolutionfile{ans}[ans1]
\begin{ex}[Quack]
First exercise
\begin{sol}
First solution.
\end{sol}
\end{ex}
\clearpage
\begin{ex}
Second exercise
\begin{sol}
Second solution.
\end{sol}
\end{ex}
\clearpage

\Closesolutionfile{ans}
\ifsolutions
\section{Solutions}
\input{ans1}
\fi
\end{document}


![Screenshot 2022-01-06 at 16.21.13.png](/image?hash=c5c6fb35cfb1d36fc5639e2972ec7c7860c1b5c2a2f19e5f8c56a8fce3d42ad5)

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