#### Answer

$0.\overline{81}=0.81818181...$

#### Work Step by Step

If we can write a fraction so that its denominator is one of 10,100, 1000,...,
we can easily write it as a decimal number
The denominator is $11$, and it is not a factor of any of the numbers mentioned.
In that case we perform division (numerator) (denominator)
$9\div 11 =$
$9.0000000\div 11=$
(after long division)
$=0.8181818181...$,
which is a periodic number with a group of two repeating digits, which we write as
$=0.\overline{81}$