Ответ:

а) \(\frac{2}{15}+\frac{5}{12}=\frac{8}{60}+\frac{25}{60}=\frac{33}{60}=\frac{11}{20}\).

б) \(\frac{3}{10}-\frac{2}{15}=\frac{9}{30}-\frac{4}{30}=\frac{5}{30}=\frac{1}{6}\).

в) \((-2\frac{1}{7})\cdot(-3,5)=(-\frac{15}{7})\cdot(-\frac{7}{2})=\frac{15}{2}=7,5\).

г) \(2,4:(-1\frac{1}{3})=\frac{12}{5}:(-\frac{4}{3})=\frac{12}{5}\cdot(-\frac{3}{4})=-\frac{9}{5}=-1,8\).

Ответ: а) \(\frac{11}{20}\); б) \(\frac{1}{6}\); в) \(7,5\); г) \(-1,8\).