54. а) (1/2 + 3/4) − (7/8 − 1/2); б) (5/9 + 2/3) − (11/18 − 1/6); в) (13/15 − 3/5) + (17/30 − 1/10); г) (5/7 − 3/14) + (25/28 − 9/14).

1. а) \(\left(\frac{1}{2}+\frac{3}{4}\right)-\left(\frac{7}{8}-\frac{1}{2}\right)=\frac{5}{4}-\frac{3}{8}=\frac{10-3}{8}=\frac{7}{8}\).
2. б) \(\left(\frac{5}{9}+\frac{2}{3}\right)-\left(\frac{11}{18}-\frac{1}{6}\right)=\frac{11}{9}-\frac{4}{9}=\frac{7}{9}\).
3. в) \(\left(\frac{13}{15}-\frac{3}{5}\right)+\left(\frac{17}{30}-\frac{1}{10}\right)=\frac{4}{15}+\frac{7}{15}=\frac{11}{15}\).
4. г) \(\left(\frac{5}{7}-\frac{3}{14}\right)+\left(\frac{25}{28}-\frac{9}{14}\right)=\frac{1}{2}+\frac{1}{4}=\frac{3}{4}\).

Ответ: а) \(\frac{7}{8}\); б) \(\frac{7}{9}\); в) \(\frac{11}{15}\); г) \(\frac{3}{4}\).