Ответ:

  1. Приведём дроби к знаменателю 6: \(3\frac{2}{3}=3\frac{4}{6}\).

    \(7\frac{5}{6}-3\frac{4}{6}=4\frac{1}{6}\).

  2. НОК знаменателей 12 и 20 равен 60:

    \(8\frac{5}{12}=8\frac{25}{60}\), \(6\frac{7}{20}=6\frac{21}{60}\).

    \(8\frac{25}{60}-6\frac{21}{60}=2\frac{4}{60}=2\frac{1}{15}\).

  3. НОК знаменателей 12 и 9 равен 36:

    \(11\frac{11}{12}=11\frac{33}{36}\), \(5\frac{7}{9}=5\frac{28}{36}\).

    \(11\frac{33}{36}-5\frac{28}{36}=6\frac{5}{36}\).

  4. НОК знаменателей 24 и 36 равен 72:

    \(9\frac{17}{24}=9\frac{51}{72}\), \(8\frac{11}{36}=8\frac{22}{72}\).

    \(9\frac{51}{72}-8\frac{22}{72}=1\frac{29}{72}\).

Ответ: 1) \(4\frac{1}{6}\); 2) \(2\frac{1}{15}\); 3) \(6\frac{5}{36}\); 4) \(1\frac{29}{72}\).