Definition of decimal numbers

The decimal numbers are formed by the integer part and the fractional part:

integer part $\leftarrow \boxed{\text{4}},\boxed{\text{39}}\to$ fractional part

To represent a decimal number as a quotient, we put all the digits of the number (integer and fractional) in the numerator, and a power of $10$ with as many zeros as fractional digits the number has in the denominator.

Within the fractional digits, we are going to differenciate:

${\displaystyle \frac{1}{10}}\to 0,1\to$ a tenth ${\displaystyle \frac{1}{100}}\to 0,01\to$ a hundredth ${\displaystyle \frac{1}{1000}}\to 0,001\to$ a thousandth