tikz number line
\documentclass[border=2pt]{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
% center the x axis
axis x line=middle,
% we don't need a y axis line ...
axis y line=none,
% ... and thus there is no need for much `height' of the axis
height=50pt,
% but `height' also changes `width' which is restored here
width=\axisdefaultwidth,
xmin=-3,
xmax=3,
]
\addplot coordinates {
(0.5,0) (0.7,0) (0.9,0)
};
\end{axis}
\end{tikzpicture}
\end{document}