а) \(\frac{3}{7}+\frac{5}{14}=\frac{6}{14}+\frac{5}{14}=\frac{11}{14}\).
б) \(\frac{8}{9}-\frac{7}{12}=\frac{32}{36}-\frac{21}{36}=\frac{11}{36}\).
в) \(\frac{11}{50}-\frac{3}{25}+\frac{1}{20}=\frac{22}{100}-\frac{12}{100}+\frac{5}{100}=\frac{15}{100}=\frac{3}{20}\).
Ответ: а) \(\frac{11}{14}\); б) \(\frac{11}{36}\); в) \(\frac{3}{20}\).