[Tex/LaTex] Why i don’t have the bar over the letter R

Question

Why I don't have the bar over the letter R?

\documentclass[11pt]{report}
\usepackage[utf8]{inputenc}

\usepackage{mathtools,array,dcolumn}

\begin{document}

\begin{equation}
Cf = 100 - (100* {\bar{R_{j(pr)}}\over{\bar{R_{j(obs)}}}})   
\end{equation}

\end{document}

Answer 1

Use \bar for short lines and \overline for longer lines.

A separate comment: In fine math typography, a \cdot is generally preferred over * to denote multiplication.

\documentclass[11pt]{report}
\usepackage[utf8]{inputenc}
\usepackage{mathtools,array}
\begin{document}

\begin{align*}
C_f 
&= 100 - 100\cdot\frac{\overline{R_{j(pr)}}}{\overline{R_{j(obs)}}} \\
&= 100 - 100\cdot\frac{\bar{R}_{j(pr)}}{\bar{R}_{j(obs)}}
\end{align*}
\end{document}