diff --git a/Advanced/Stopping Problems/parts/0 probability.tex b/Advanced/Stopping Problems/parts/0 probability.tex
index 3e52975..e75b9da 100644
--- a/Advanced/Stopping Problems/parts/0 probability.tex	
+++ b/Advanced/Stopping Problems/parts/0 probability.tex	
@@ -60,6 +60,9 @@ As a function, $\mathcal{H}$ maps values in $\Omega$ to values in $\mathbb{Z}^+_
 	\item ...and so on.
 \end{itemize}
 
+Intuitively, a random variable assigns a \say{value} in $\mathbb{R}$ to every possible outcome.
+
+
 \definition{}
 We can compute the probability that a random variable takes a certain value by computing the probability of
 the set of outcomes that produce that value. \par
@@ -92,18 +95,18 @@ Find $\mathcal{P}(\mathcal{X} = x)$ for all $x$ in $\mathbb{Z}$.
 %
 
 
-\definition{}
+\definition{}<defexp>
 Say we have a random variable $\mathcal{X}$ that produces outputs in $\mathbb{R}$. \par
 The \textit{expected value} of $\mathcal{X}$ is then defined as
 \begin{equation*}
 	\mathcal{E}(\mathcal{X})
-	~\coloneqq~ \sum_{x \in A}\Bigl(x \times \mathcal{P}\bigl(\mathcal{X} = x\bigr)\Bigr)
+	~\coloneqq~ \sum_{x \in \mathbb{R}}\Bigl(x \times \mathcal{P}\bigl(\mathcal{X} = x\bigr)\Bigr)
 	~=~ \sum_{\omega \in \Omega}\Bigl(\mathcal{X}(\omega) \times \mathcal{P}(\omega)\Bigr)
 \end{equation*}
 That is, $\mathcal{E}(\mathcal{X})$ is the average of all possible outputs of $\mathcal{X}$ weighted by their probability.
 
 \problem{}
-Say we flip a coin with $\mathcal{P}(\texttt{H}) = \nicefrac{1}{3}$ three times. \par
+Say we flip a coin with $\mathcal{P}(\texttt{H}) = \nicefrac{1}{3}$ two times. \par
 Define $\mathcal{H}$ as the number of heads we see. \par
 Find $\mathcal{E}(\mathcal{H})$.
 
@@ -113,6 +116,14 @@ Find $\mathcal{E}(\mathcal{H})$.
 Let $\mathcal{A}$ and $\mathcal{B}$ be two random variables. \par
 Show that $\mathcal{E}(\mathcal{A} + \mathcal{B}) = \mathcal{E}(\mathcal{A}) + \mathcal{E}(\mathcal{B})$.
 
+\begin{solution}
+	Use the second definition of $\mathcal{E}$, $\sum_{\omega \in \Omega}\Bigl(\mathcal{X}(\omega) \times \mathcal{P}(\omega)\Bigr)$.
+
+	\vspace{2mm}
+
+	Make sure students understand all parts of \ref{defexp}, and are comfortable with the fact that a random variable \say{assigns values} to outcomes.
+\end{solution}
+
 \vfill
 
 \definition{}
diff --git a/resources/share/main.tex b/resources/share/main.tex
new file mode 100755
index 0000000..b091bd5
--- /dev/null
+++ b/resources/share/main.tex
@@ -0,0 +1,35 @@
+% use [nosolutions] flag to hide solutions.
+% use [solutions] flag to show solutions.
+\documentclass[
+	solutions,
+	singlenumbering
+]{./ormc_handout}
+
+
+\title{The Size of Sets}
+\subtitle{Prepared by Mark on \today{}}
+
+\begin{document}
+
+	\maketitle
+
+	\section{Set Basics}
+
+	\definition{}
+	A \textit{set} is a collection of objects. \par
+	If $a$ is an element of set $S$, we write $a \in S$. This is pronounced \say{$a$ in $S$.} \par
+	The position of each element in a set or the number of times it is repeated doesn't matter. \par
+	All that matters is \textit{which} elements are in the set.
+
+	\vspace{2mm}
+
+	We say two sets $A$ and $B$ are equal if every element of $A$ is in $B$, and every element of $B$ is in $A$. This is known as the \textit{principle of extensionality.}
+
+	\problem{}
+	Convince yourself that $\{a, b\} = \{b, a\} = \{a, b, a, b, b\}$.
+
+	\begin{solution}
+		This is a solution.
+	\end{solution}
+
+\end{document}
\ No newline at end of file