Date le frazioni $\displaystyle \frac{a}{b}$ e $\displaystyle \frac{c}{d}$:

$\displaystyle \frac{a}{b}<\frac{c}{d}$, se $a\cdot d < b\cdot c$;

$\displaystyle \frac{a}{b}>\frac{c}{d}$, se $a\cdot d > b\cdot c$;

$\displaystyle \frac{a}{b}=\frac{c}{d}$, se $a\cdot d = b\cdot c$.

Esempio.
$\displaystyle \frac{4}{5}<\frac{7}{8}$, infatti $4\cdot 8 <7\cdot 5$

$\displaystyle \frac{6}{7}>\frac{3}{4}$, infatti $6\cdot 4 >3\cdot 7$

$\displaystyle \frac{6}{7}=\frac{12}{14}$, infatti $6\cdot 14 =12\cdot 7$