Решение:

а) $$\frac{7}{35} + \frac{1}{14} = \frac{1}{5} + \frac{1}{14} = \frac{14}{70} + \frac{5}{70} = \frac{19}{70}$$

б) $$7 - 3\frac{2}{9} = 7 - \frac{29}{9} = \frac{63}{9} - \frac{29}{9} = \frac{34}{9} = 3\frac{7}{9}$$

в) $$-7 \cdot \frac{9}{14} = - \frac{7}{1} \cdot \frac{9}{14} = - \frac{1}{1} \cdot \frac{9}{2} = -\frac{9}{2} = -4\frac{1}{2}$$

г) $$\frac{3}{25} \cdot (-\frac{20}{21}) = -\frac{3}{25} \cdot \frac{20}{21} = -\frac{3 \cdot 20}{25 \cdot 21} = -\frac{3 \cdot 4 \cdot 5}{5 \cdot 5 \cdot 3 \cdot 7} = -\frac{4}{35}$$

д) $$-3\frac{3}{4} \cdot 1\frac{3}{5} = -\frac{15}{4} \cdot \frac{8}{5} = -\frac{15 \cdot 8}{4 \cdot 5} = -\frac{3 \cdot 5 \cdot 2 \cdot 4}{4 \cdot 5} = -6$$

Ответ:

• a) $$\frac{19}{70}$$
• б) $$3\frac{7}{9}$$
• в) $$-4\frac{1}{2}$$
• г) $$\frac{-4}{35}$$
• д) $$-6$$