55. а) (13/18 + 1/3) − (5/27 − 1/6); б) (11/45 − 1/9) + (12/15 − 3/10); в) (7/16 + 3/8) − (7/8 − 27/32); г) (8/21 + 11/14) − (4/7 − 5/14).

1. а) \(\left(\frac{13}{18}+\frac{1}{3}\right)-\left(\frac{5}{27}-\frac{1}{6}\right)=\frac{19}{18}-\frac{1}{54}=\frac{57-1}{54}=\frac{28}{27}\).
2. б) \(\left(\frac{11}{45}-\frac{1}{9}\right)+\left(\frac{12}{15}-\frac{3}{10}\right)=\frac{2}{15}+\frac{1}{2}=\frac{19}{30}\).
3. в) \(\left(\frac{7}{16}+\frac{3}{8}\right)-\left(\frac{7}{8}-\frac{27}{32}\right)=\frac{13}{16}-\frac{1}{32}=\frac{25}{32}\).
4. г) \(\left(\frac{8}{21}+\frac{11}{14}\right)-\left(\frac{4}{7}-\frac{5}{14}\right)=\frac{7}{6}-\frac{3}{14}=\frac{20}{21}\).

Ответ: а) \(\frac{28}{27}\); б) \(\frac{19}{30}\); в) \(\frac{25}{32}\); г) \(\frac{20}{21}\).