а) $$ \frac{5}{8} + \frac{3}{16} = \frac{5 \cdot 2}{8 \cdot 2} + \frac{3}{16} = \frac{10}{16} + \frac{3}{16} = \frac{10+3}{16} = \frac{13}{16} $$
в) $$ 1 \frac{2}{9} \cdot \frac{3}{8} = \frac{11}{9} \cdot \frac{3}{8} = \frac{11 \cdot 3}{9 \cdot 8} = \frac{11 \cdot 1}{3 \cdot 8} = \frac{11}{24} $$
Ответ: а) $$ \frac{13}{16} $$ , в) $$ \frac{11}{24} $$