11. Выполните действия: 1) 7/12 − 4/30; 2) 8/21 + 5/14; 3) 3/4 − 1/18; 4) 7/12 − 2/9.

1. \(\frac{7}{12}-\frac{4}{30}=\frac{35}{60}-\frac{8}{60}=\frac{27}{60}=\frac{9}{20}\).
2. \(\frac{8}{21}+\frac{5}{14}=\frac{16}{42}+\frac{15}{42}=\frac{31}{42}\).
3. \(\frac{3}{4}-\frac{1}{18}=\frac{27}{36}-\frac{2}{36}=\frac{25}{36}\).
4. \(\frac{7}{12}-\frac{2}{9}=\frac{21}{36}-\frac{8}{36}=\frac{13}{36}\).

Ответ: 1) \(\frac{9}{20}\); 2) \(\frac{31}{42}\); 3) \(\frac{25}{36}\); 4) \(\frac{13}{36}\).