[tex]\frac{-3}{10}+\frac{5}{12}-\frac{7}{20}=\\ \\ =\frac{-3\cdot 6}{60}+\frac{5\cdot 5}{60}-\frac{7\cdot 3}{60}=\\ \\ =\frac{-18+25-21}{60}=\\ \\ =\frac{-39+25}{60}=\\ \\=\frac{-14}{60}=\frac{-7}{30}[/tex]
Am amplificat prima fractie cu 6, a doua cu 5 si a treia cu 3
