Answer
$=\dfrac {5}{9}$
Work Step by Step
$0.\overline {5}=0.555...=\dfrac {5}{10}+\dfrac {5}{10^{2}}+\dfrac {5}{10^{3}}+\dfrac {}{..}=\dfrac {a_{1}}{1-r}=\dfrac {\dfrac {5}{10}}{1-\dfrac {1}{10}}=\dfrac {\dfrac {5}{10}}{\dfrac {9}{10}}=\dfrac {5}{9}$