# How do I align the equations about the equal to sign, with lines of text in between? [duplicate]

I want to align unnumbered equations about the '=' sign having one or two lines of statements in between. And also, I want them to be centered. Here is what I did in my code:

\begin{align*}
T & = \frac{0.161V}{\sum as}\\
\sum as & = \frac{0.161V}{T}\\
\end{align*}
Substituting the known values, we get,\\
\begin{align*}
\sum as & = \frac{0.161 \times 120000}{1.5}\\
\sum as & = 13360 \text{ O W U}
\end{align*}
The total absorption of the hall is 13,360 open window units (O W U)\\
Therefore, the average absorbing power of the surface\\
\begin{align*}
a & = \frac{\sum as}{\sum s}\\
\implies a & = \frac{13360}{25000}\\
\implies a &=0.5344 \text{sabine}
\end{align*}
The average absorbing power of the surface is 0.5344 sabine.


The above code gives an output in which the equal to signs are not aligned. I want them to be centered and aligned. Also the equation comes in the next line of the statement. I want them to come in a single line. Please help.

• Welcome to the site. If you indent your code by 4 spaces, it displays in a code-like format. Alternately, you can highlight the left-aligned code, and click the braces icon above the edit box, which will indent the highlighted code for you. – Steven B. Segletes Oct 1 '14 at 12:02
• Put everything in one align an use \intertext for the text in between? – moewe Oct 1 '14 at 12:08
• as @moewe said use \intertext but also remove the \\  from before the align you only want \\  inside the alignment. – David Carlisle Oct 1 '14 at 12:22
• this question addresses the same issue: How can I break an align environment for a paragraph? – barbara beeton Oct 1 '14 at 13:06

The solution has already been mentioned in the comments. I introduced the great package siunitx here, as it prints numbers nicer and gets the spacing for units right. I also declared two new units for you. If you decide later that \text{sabine} should become \mathscr{S} or whatever, you can change this for your whole document with just one edit.

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}
\usepackage{siunitx}
\DeclareSIUnit{\sabine}{\text{sabine}}
\DeclareSIUnit{\owu}{\text{OWU}}

\begin{document}
\begin{align*}
T &= \frac{0.161 V}{\sum as}\\
\sum as &= \frac{0.161 V}{T}\\
\intertext{Substituting the known values, we get,}
\sum as &= \frac{0.161 \times 120000}{1.5}\\
\sum as &= \SI{13360}{\owu}
\intertext{The total absorption of the hall is \num{13360} open window units (\si{\owu}).
Therefore, the average absorbing power of the surface is:}
a & = \frac{\sum as}{\sum s}\\
\smashoperator{\implies} a &= \frac{13360}{25000}\\
\smashoperator{\implies} a &= \SI{0.5344}{\sabine}
\end{align*}
The average absorbing power of the surface is \SI{0.5344}{\sabine}.
\end{document}
`