4. Выполни действия, используя правило сложения и вычитания дробей с разными знаменателями.

Решение:

1. \( \frac{2}{7} - \frac{1}{8} = \frac{16 - 7}{56} = \frac{9}{56} \)
2. \( \frac{3}{4} - \frac{2}{7} = \frac{21 - 8}{28} = \frac{13}{28} \)
3. \( \frac{8}{9} - \frac{1}{2} = \frac{16 - 9}{18} = \frac{7}{18} \)
4. \( \frac{19}{45} - \frac{7}{60} = \frac{76 - 21}{180} = \frac{55}{180} = \frac{11}{36} \)
5. \( \frac{7}{36} + \frac{1}{6} = \frac{7 + 6}{36} = \frac{13}{36} \)
6. \( \frac{6}{35} - \frac{2}{49} = \frac{42 - 10}{245} = \frac{32}{245} \)
7. \( \frac{8}{9} + \frac{2}{3} = \frac{8 + 6}{9} = \frac{14}{9} \)
8. \( \frac{11}{25} + \frac{4}{5} = \frac{11 + 20}{25} = \frac{31}{25} \)
9. \( \frac{121}{4} + \frac{77}{4} = \frac{198}{4} = \frac{99}{2} \)
10. \( \frac{5}{27} - \frac{4}{24} = \frac{5}{27} - \frac{1}{6} = \frac{10 - 9}{54} = \frac{1}{54} \)
11. \( \frac{15}{36} - \frac{7}{60} = \frac{5}{12} - \frac{7}{60} = \frac{25 - 7}{60} = \frac{18}{60} = \frac{3}{10} \)
12. \( \frac{20}{21} - \frac{13}{35} = \frac{100 - 39}{105} = \frac{61}{105} \)

Ответ:
\( \frac{9}{56} \), \( \frac{13}{28} \), \( \frac{7}{18} \), \( \frac{11}{36} \),
\( \frac{13}{36} \), \( \frac{32}{245} \), \( \frac{14}{9} \), \( \frac{31}{25} \),
\( \frac{99}{2} \), \( \frac{1}{54} \), \( \frac{3}{10} \), \( \frac{61}{105} \).