56. а) (7/18 − 1/9) + (5/6 − 7/12); б) (17/25 + 3/5) − (29/50 − 3/10); в) (13/27 + 2/9) − (11/21 + 1/7); г) (14/15 − 3/5) − (11/12 − 3/4).

1. а) \(\left(\frac{7}{18}-\frac{1}{9}\right)+\left(\frac{5}{6}-\frac{7}{12}\right)=\frac{5}{18}+\frac{1}{4}=\frac{19}{36}\).
2. б) \(\left(\frac{17}{25}+\frac{3}{5}\right)-\left(\frac{29}{50}-\frac{3}{10}\right)=\frac{32}{25}-\frac{7}{25}=1\).
3. в) \(\left(\frac{13}{27}+\frac{2}{9}\right)-\left(\frac{11}{21}+\frac{1}{7}\right)=\frac{19}{27}-\frac{2}{3}=\frac{1}{27}\).
4. г) \(\left(\frac{14}{15}-\frac{3}{5}\right)-\left(\frac{11}{12}-\frac{3}{4}\right)=\frac{1}{3}-\frac{1}{6}=\frac{1}{6}\).

Ответ: а) \(\frac{19}{36}\); б) \(1\); в) \(\frac{1}{27}\); г) \(\frac{1}{6}\).