Multiline equations in LaTeX

Law of Large Numbers for Binomial.tex

\usepackage{amsmath}
% lazy numbering for aling*:
\newcommand{\numberthis}{\addtocounter{equation}{1}\tag{\theequation}}

%in the document:
\begin{align*}
 &\Pb{X_n > n(p + \epsilon)} = \sum_{j = K}^{n} \Pb{X_n = j} \\
 &\leq \sum_{j = K}^{n} \Pb{X_n = K} r_K ^{j-K} 
 \leq \sum_{j = K}^{\infty} \Pb{X_n = K} r_K ^{j-K} \\
 &= \Pb{X_n = K} \cdot \frac{1}{1 - r_K} \numberthis \label{eq:bound}
\end{align*}