Решение:
а) $\frac{7}{25} - \frac{11}{25} - \frac{2}{25} = -(\frac{7}{25} + \frac{11}{25} + \frac{2}{25}) = -\frac{7 + 11 + 2}{25} = -\frac{20}{25} = -\frac{4}{5}$;
б) $-\frac{1}{72} - \frac{7}{72} - \frac{18}{72} = -(\frac{1}{72} + \frac{7}{72} + \frac{18}{72}) = -\frac{1 + 7 + 18}{72} = -\frac{26}{72} = -\frac{13}{36}$;
в) $-\frac{19}{55} - \frac{18}{55} + \frac{4}{55} = -(\frac{19}{55} + \frac{18}{55}) + \frac{4}{55} = -\frac{19 + 18}{55} + \frac{4}{55} = -\frac{37}{55} + \frac{4}{55} = -(\frac{37}{55} - \frac{4}{55}) = -\frac{33}{55} = -\frac{3}{5}$;
г) $\frac{25}{64} - \frac{17}{64} - \frac{15}{64} = (\frac{25}{64} - \frac{15}{64}) - \frac{17}{64} = \frac{10}{64} - \frac{17}{64} = -\frac{7}{64}$.
Ответ:
а) $-\frac{4}{5}$;
б) $-\frac{13}{36}$;
в) $-\frac{3}{5}$;
г) $-\frac{7}{64}$.