Aligning two different align* environments

Question

My question is, how can I get the two different align* environments to agree on the equal signs being centred for all six equations on the page (even though there is a line of text breaking them into groups of three and three):

Answer 1

Do you mean like this?

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}
\DeclareMathOperator{\var}{Var}

\begin{document}
\begin{align*}
    E(M) &= A\\
    E(A) &= 180-B-C\\
    E(N) &= A/2 - B/2 - C/2 + 90
    \intertext{(b) The variances are given by:}
    \var(M) &= 1\\
    \var(A) &= 1/2\\
    \var(N) &= 3/4
\end{align*}
\end{document}

---

Update:

If the other commentators are right and you are inside an itemize environment, a very easy solution would be to define your own indent. Not super fancy, but clear and easy.

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}
\DeclareMathOperator{\var}{Var}
\newcommand*{\myIndent}{\hspace{4cm}} % or whatever space you may find on http://tex.stackexchange.com/a/74354

\begin{document}
\begin{itemize}
    \item[(a)] Whatever you have written in item (a):
    \begin{flalign*}
    \myIndent\mathllap{E(M)} &= A&\\
    E(A) &= 180-B-C\\
    E(N) &= A/2 - B/2 - C/2 + 90
    \end{flalign*}
    \item[(b)] The variances are given by:
    \begin{flalign*}
    \myIndent\mathllap{\var(M)} &= 1&\\
    \var(A) &= 1/2\\
    \var(N) &= 3/4
    \end{flalign*}
\end{itemize}
\end{document}

---

Update 2:

daleif brought me to the idea to use \item directly in \intertext (or \shortintertext, if you prefer the vertical spacing). You will need at least one \item outside the align in order to get that working.

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}
\DeclareMathOperator{\var}{Var}
\usepackage{enumitem}
\usepackage{blindtext}

\begin{document}
\begin{enumerate}[label=(\alph*)]
    \item \blindtext
    \begin{align*}
        E(M) &= A\\
        E(A) &= 180-B-C\\
        E(N) &= A/2 - B/2 - C/2 + 90
        \intertext{\item The variances are given by:}
        \var(M) &= 1\\
        \var(A) &= 1/2\\
        \var(N) &= 3/4
    \end{align*}
\end{enumerate}
\end{document}