54.78-1217

54. $$\frac{7}{15} - 12\frac{17}{30} = \frac{7}{15} - \frac{377}{30} = \frac{14}{30} - \frac{377}{30} = \frac{-363}{30} = -12\frac{3}{30} = -12\frac{1}{10}$$

Ответ: $$-12\frac{1}{10}$$