a) $$17\frac{7}{8} + \frac{5}{6} = 17\frac{21}{24} + \frac{20}{24} = 17\frac{41}{24} = 18\frac{17}{24}$$
б) $$0,45 : \frac{9}{2} = \frac{45}{100} : \frac{9}{2} = \frac{45}{100} \cdot \frac{2}{9} = \frac{5}{50} = \frac{1}{10} = 0,1$$
Ответ: a) $$18\frac{17}{24}$$, б) 0,1