а) 1/5 + 1/3

а) $\frac{1}{5} + \frac{1}{3} = \frac{3}{15} + \frac{5}{15} = \frac{8}{15}$ б) $\frac{1}{2} + \frac{3}{8} = \frac{4}{8} + \frac{3}{8} = \frac{7}{8}$ в) $\frac{3}{4} + 2 = \frac{3}{4} + \frac{8}{4} = \frac{11}{4} = 2\frac{3}{4}$ г) $\frac{2}{3} - \frac{1}{6} = \frac{4}{6} - \frac{1}{6} = \frac{3}{6} = \frac{1}{2}$ д) $\frac{7}{12} - 1 = \frac{7}{12} - \frac{12}{12} = -\frac{5}{12}$ е) $\frac{4}{5} - \frac{9}{10} = \frac{8}{10} - \frac{9}{10} = -\frac{1}{10}$ ё) $\frac{1}{3} - \frac{1}{2} = \frac{2}{6} - \frac{3}{6} = -\frac{1}{6}$ ж) $1 + \frac{1}{3} = \frac{3}{3} + \frac{1}{3} = \frac{4}{3} = 1\frac{1}{3}$ з) $\frac{8}{15} : 4 = \frac{8}{15} \cdot \frac{1}{4} = \frac{2}{15}$ и) $3 : \frac{3}{2} = 3 \cdot \frac{2}{3} = 2$ й) $1 : \frac{3}{4} = 1 \cdot \frac{4}{3} = \frac{4}{3} = 1\frac{1}{3}$ к) $\frac{7}{12} : (-\frac{1}{4}) = \frac{7}{12} \cdot (-4) = -\frac{28}{12} = -\frac{7}{3} = -2\frac{1}{3}$ л) $\frac{1}{4} \cdot 2 = \frac{2}{4} = \frac{1}{2}$ м) $\frac{3}{4} \cdot \frac{4}{9} = \frac{1}{1} \cdot \frac{1}{3} = \frac{1}{3}$ н) $\frac{7}{9} \cdot \frac{18}{35} = \frac{1}{1} \cdot \frac{2}{5} = \frac{2}{5}$ о) $-\frac{4}{19} \cdot (-\frac{57}{64}) = \frac{4}{19} \cdot \frac{57}{64} = \frac{1}{1} \cdot \frac{3}{16} = \frac{3}{16}$