Addizioni e sottrazioni

$\displaystyle +\frac{3}{7}-\left( -\frac{1}{4}\right) +\left(- \frac{1}{2}\right) =\frac{3}{7}+\frac{1}{4}-\frac{1}{2}=\frac{12+7-14}{28}=\frac{5}{28}$

Moltiplicazioni

$\displaystyle \left(+\frac{4}{7}\right)\cdot \left(-\frac{3}{4}\right)\cdot \left( +\frac{1}{3}\right)=-\frac{4\cdot 3\cdot 1}{7\cdot 4\cdot 3}=-\frac{1}{7}$

Divisioni

$\displaystyle \left( +\frac{4}{7}\right) : \left( -\frac{5}{7}\right) = \left( +\frac{4}{7}\right) \cdot \left( -\frac{7}{5}\right)=-\frac{4\cdot 7}{7\cdot 5}=-\frac{4}{5}$