3. Выполните действия, применив правила сложения и вычитания дробей с разными знаменателями: а) \(\frac{3}{8}+\frac{9}{20}\); б) \(\frac{5}{6}-\frac{1}{2}\); в) \(\frac{3}{5}-\frac{4}{7}\); г) \(\frac{7}{12}-\frac{3}{20}\); д) \(\frac{6}{7}-\frac{14}{49}\); е) \(\frac{19}{60}-\frac{3}{20}\); ж) \(\frac{29}{30}-\frac{7}{15}\); з) \(\frac{2}{3}-\frac{2}{5}+\frac{1}{4}\); и) \(\frac{7}{15}+\frac{2}{5}-\frac{2}{3}\); к) \(\frac{1}{4}+\frac{5}{6}-\frac{5}{12}\).

1. а) \(\frac{3}{8}+\frac{9}{20}=\frac{15}{40}+\frac{18}{40}=\frac{33}{40}\);
2. б) \(\frac{5}{6}-\frac{1}{2}=\frac{5}{6}-\frac{3}{6}=\frac{2}{6}=\frac{1}{3}\);
3. в) \(\frac{3}{5}-\frac{4}{7}=\frac{21}{35}-\frac{20}{35}=\frac{1}{35}\);
4. г) \(\frac{7}{12}-\frac{3}{20}=\frac{35}{60}-\frac{9}{60}=\frac{26}{60}=\frac{13}{30}\);
5. д) \(\frac{6}{7}-\frac{14}{49}=\frac{42}{49}-\frac{14}{49}=\frac{28}{49}=\frac{4}{7}\);
6. е) \(\frac{19}{60}-\frac{3}{20}=\frac{19}{60}-\frac{9}{60}=\frac{10}{60}=\frac{1}{6}\);
7. ж) \(\frac{29}{30}-\frac{7}{15}=\frac{29}{30}-\frac{14}{30}=\frac{15}{30}=\frac{1}{2}\);
8. з) \(\frac{2}{3}-\frac{2}{5}+\frac{1}{4}=\frac{40}{60}-\frac{24}{60}+\frac{15}{60}=\frac{31}{60}\);
9. и) \(\frac{7}{15}+\frac{2}{5}-\frac{2}{3}=\frac{7}{15}+\frac{6}{15}-\frac{10}{15}=\frac{3}{15}=\frac{1}{5}\);
10. к) \(\frac{1}{4}+\frac{5}{6}-\frac{5}{12}=\frac{3}{12}+\frac{10}{12}-\frac{5}{12}=\frac{8}{12}=\frac{2}{3}\).

Ответ: а) \(\frac{33}{40}\); б) \(\frac{1}{3}\); в) \(\frac{1}{35}\); г) \(\frac{13}{30}\); д) \(\frac{4}{7}\); е) \(\frac{1}{6}\); ж) \(\frac{1}{2}\); з) \(\frac{31}{60}\); и) \(\frac{1}{5}\); к) \(\frac{2}{3}\).