It is simplifying the ratio.
simplifying
Divide the numerator and denominator of the ratio by their highest common factor.
It is one way to simplify the ratio.
It gives an equivalent ratio is a simpler form.
It could be simplifying the fraction.
You divide the numerator by the denominator.
You divide the numerator of the ratio by its denominator.
It means that the previous fraction was not in its lowest terms.
Divide the numerator and denominator of the fraction by their greatest common factor.
They are a common factor and any common factor in the numerator and denominator of a ratio can be cancelled out.
Dividing the numerator and denominator by a common factor is how you simplify a fraction.