Ответ:
- \(8\frac{9}{11}-8\frac{3}{7}=\frac{9}{11}-\frac{3}{7}=\frac{63-33}{77}=\frac{30}{77}\).
- \(3\frac{7}{21}=3\frac{1}{3}=3\frac{4}{12}\), поэтому \(7\frac{5}{12}-3\frac{4}{12}=4\frac{1}{12}\).
- \(12\frac{11}{12}=11\frac{33}{36}\), \(5\frac{13}{18}=5\frac{26}{36}\). Тогда \(11\frac{33}{36}-5\frac{26}{36}=6\frac{7}{36}\).
Ответ: 1) \(\frac{30}{77}\); 2) \(4\frac{1}{12}\); 3) \(6\frac{7}{36}\).
