Решение:
а) $\frac{8}{9} * \frac{7}{24} - \frac{8}{9} * \frac{5}{24} = \frac{8}{9} * (\frac{7}{24} - \frac{5}{24}) = \frac{8}{9} * \frac{2}{24} = \frac{8}{9} * \frac{1}{12} = \frac{2 * 1}{9 * 3} = \frac{2}{27}$;
б) $\frac{3}{25} * (-\frac{5}{49}) + \frac{22}{25} * (-\frac{5}{49}) = (-\frac{5}{49}) * (\frac{3}{25} + \frac{22}{25}) = (-\frac{5}{49}) * \frac{25}{25} = (-\frac{5}{49}) * 1 = -\frac{5}{49}$.
Ответ:
а) $\frac{2}{27}$;
б) $-\frac{5}{49}$.