2. $$\frac{7}{15}:(\frac{6}{10}-\frac{8}{3})+19 \cdot \frac{2}{31}$$ 4. $$(1\frac{1}{35}:\frac{4}{5}-1\frac{8}{35}) \cdot 3\frac{1}{3}$$ 6. $$2\frac{7}{9} \cdot \frac{18}{25}+\frac{9}{60}:(\frac{7}{12}-\frac{3}{5})$$ 8. $$(\frac{4}{5}+\frac{4}{7}) \cdot (3\frac{3}{8}+2\frac{11}{4})$$ 10. $$-3\frac{1}{7} \cdot (-8)-2,9:0,1 + \frac{11}{21}:(-3\frac{2}{3})$$ 12. $$(6-2\frac{4}{5}) \cdot 3\frac{1}{8}-1\frac{3}{5}:\frac{1}{4}$$

Выполняю вычисления по порядку. 2. $$\frac{7}{15}:(\frac{6}{10}-\frac{8}{3})+19 \cdot \frac{2}{31} = \frac{7}{15}:(\frac{18}{30}-\frac{80}{30})+19 \cdot \frac{2}{31} = \frac{7}{15}:(-\frac{62}{30})+\frac{38}{31} =$$ $$=-\frac{7}{15} \cdot \frac{30}{62} + \frac{38}{31} = -\frac{7}{1} \cdot \frac{2}{62} + \frac{38}{31} = -\frac{14}{62} + \frac{38}{31} = -\frac{7}{31} + \frac{38}{31} = \frac{31}{31} = 1$$ Ответ: 1 4. $$(1\frac{1}{35}:\frac{4}{5}-1\frac{8}{35}) \cdot 3\frac{1}{3} = (\frac{36}{35}:\frac{4}{5}-\frac{43}{35}) \cdot \frac{10}{3} = (\frac{36}{35} \cdot \frac{5}{4} - \frac{43}{35}) \cdot \frac{10}{3} = $$ $$=(\frac{9}{7} \cdot \frac{1}{1} - \frac{43}{35}) \cdot \frac{10}{3} = (\frac{45}{35} - \frac{43}{35}) \cdot \frac{10}{3} = \frac{2}{35} \cdot \frac{10}{3} = \frac{2}{7} \cdot \frac{2}{3} = \frac{4}{21}$$ Ответ: $$\frac{4}{21}$$ 6. $$2\frac{7}{9} \cdot \frac{18}{25}+\frac{9}{60}:(\frac{7}{12}-\frac{3}{5}) = \frac{25}{9} \cdot \frac{18}{25} + \frac{3}{20}:(\frac{35}{60}-\frac{36}{60}) = \frac{2}{1} + \frac{3}{20}:(-\frac{1}{60}) = $$ $$= 2 + \frac{3}{20} \cdot (-60) = 2 - \frac{3}{1} \cdot (3) = 2 - 9 = -7$$ Ответ: -7 8. $$(\frac{4}{5}+\frac{4}{7}) \cdot (3\frac{3}{8}+2\frac{11}{4}) = (\frac{28}{35}+\frac{20}{35}) \cdot (\frac{27}{8}+ \frac{19}{4}) = \frac{48}{35} \cdot (\frac{27}{8}+\frac{38}{8}) =$$ $$= \frac{48}{35} \cdot \frac{65}{8} = \frac{6}{7} \cdot \frac{13}{1} = \frac{78}{7} = 11\frac{1}{7}$$ Ответ: $$11\frac{1}{7}$$ 10. $$-3\frac{1}{7} \cdot (-8)-2,9:0,1 + \frac{11}{21}:(-3\frac{2}{3}) = -\frac{22}{7} \cdot (-8) - 29 + \frac{11}{21}:(-\frac{11}{3}) = $$ $$=\frac{176}{7} - 29 + \frac{1}{7} \cdot (- \frac{1}{1}) = \frac{176}{7} - 29 - \frac{1}{7} = \frac{175}{7} - 29 = 25 - 29 = -4$$ Ответ: -4 12. $$(6-2\frac{4}{5}) \cdot 3\frac{1}{8}-1\frac{3}{5}:\frac{1}{4} = (6 - \frac{14}{5}) \cdot \frac{25}{8} - \frac{8}{5}:\frac{1}{4} = (\frac{30}{5} - \frac{14}{5}) \cdot \frac{25}{8} - \frac{8}{5} \cdot 4 =$$ $$=\frac{16}{5} \cdot \frac{25}{8} - \frac{32}{5} = \frac{2}{1} \cdot \frac{5}{1} - \frac{32}{5} = 10 - \frac{32}{5} = \frac{50}{5} - \frac{32}{5} = \frac{18}{5} = 3\frac{3}{5}$$ Ответ: $$3\frac{3}{5}$$