### Theory:

In practice, decimal fractions are more often used. Still, when both ordinary and decimal fractions are encountered in the problem, one should switch to one type of fraction (convert decimal fractions to ordinary or ordinary to decimal). Not always an ordinary fraction can be converted to decimal, so the decimal is converted to ordinary.
The unit digit in the denominator ($$10, 100, 1000$$, etc) of the ordinary fraction contains as many zeros as decimal places in the decimal number.
We convert decimal fractions of $$0.3; 0.17; 0.231; 0.0007$$ to an ordinary fraction.
In the first fraction, $$0.3$$ has one decimal place, so we have $$10$$ in the denominator.
Among them $$0.17$$ has two decimal places, so we have $$100$$ in the denominator, etc.

$\begin{array}{l}0.3=\frac{3}{10};\\ 0.17=\frac{17}{100};\\ 0.231=\frac{231}{1000};\\ 0.0007=\frac{7}{10000}.\end{array}$

If the decimal fraction contains the integer part, then it is converted to a mixed number and the integer part is written before the fractional part.

$\begin{array}{l}15.3=15\frac{3}{10};\\ 6.0019=6\frac{19}{10000}.\end{array}$