How do you write 0.09 as a fraction?

A fraction with 10 to a power in the denominator can be used to express every place value after the decimal point.
The "tenths place" is the first position following the decimal point. I would have 9 tenths, or as a fraction, if I had 0.9 - ${\displaystyle \frac{9}{10}}$ 
The "hundredths place" is the position immediately following the decimal point. The query above requests ${\displaystyle 0.09}$. This would be in fractional units of nine hundredths ${\displaystyle \frac{9}{100}}$

Because every decimal turns to a fraction with a denominator of 10 or a power of 10, I like dealing with decimals.
More zeros are simply added to make a power of 10.
${\displaystyle 10,100,1000\dots }$
You will notice a pattern after dealing with a couple of these examples.
To produce a fraction from the provided number, you will need as many zeros in the denominator as there are decimal places in the value.
With two decimal places, ${\displaystyle 0.09}$ will give us the whole number 9 for the numerator. That means the denominator will have two zeros to give ${\displaystyle \frac{1}{100}}$
${\displaystyle 0.09=\frac{9}{100}}$
Try also converting ${\displaystyle 0.1085}$ to a fraction.
Numerator is ${\displaystyle 1085\text{and}therefourzerostogive\frac{1}{10000}}$
${\displaystyle 0.1085=\frac{1085}{10000}}$ which simplifies to ${\displaystyle \frac{217}{2000}}$
What about decimal values higher than one?
Convert ${\displaystyle 25.492}$ to a fraction.
The decimal portion must be expressed as a fraction because the entire number is already 25.
Three decimal places are present and the numerator is 492.
Now, the denominator needs three zeros to equal one. ${\displaystyle \frac{1}{1000}}$
${\displaystyle 25.492=25\frac{492}{1000}}$ which simplifies to ${\displaystyle 25\frac{123}{250}}$