e) 3+5 7 11 ж) 6.5 25 18 3)3-1음 и) 4.5 7 9 к) 3.9 8 16 л) 7:3음

e) $$ \frac{3}{7} + \frac{5}{11} = \frac{3 \cdot 11}{7 \cdot 11} + \frac{5 \cdot 7}{11 \cdot 7} = \frac{33}{77} + \frac{35}{77} = \frac{33 + 35}{77} = \frac{68}{77} $$

ж) $$ \frac{6}{25} \cdot \frac{5}{18} = \frac{6 \cdot 5}{25 \cdot 18} = \frac{6 \cdot 5}{5 \cdot 5 \cdot 6 \cdot 3} = \frac{1}{5 \cdot 3} = \frac{1}{15} $$

з) $$ 3 \frac{3}{5} \cdot 1 \frac{1}{9} = \frac{3 \cdot 5 + 3}{5} \cdot \frac{1 \cdot 9 + 1}{9} = \frac{18}{5} \cdot \frac{10}{9} = \frac{18 \cdot 10}{5 \cdot 9} = \frac{9 \cdot 2 \cdot 5 \cdot 2}{5 \cdot 9} = 2 \cdot 2 = 4 $$

и) $$ \frac{4}{7} : \frac{5}{9} = \frac{4}{7} \cdot \frac{9}{5} = \frac{4 \cdot 9}{7 \cdot 5} = \frac{36}{35} = 1 \frac{1}{35} $$

к) $$ \frac{3}{8} \cdot \frac{9}{16} = \frac{3 \cdot 9}{8 \cdot 16} = \frac{27}{128} $$

л) $$ 7 \frac{11}{12} : 3 \frac{1}{6} = \frac{7 \cdot 12 + 11}{12} : \frac{3 \cdot 6 + 1}{6} = \frac{95}{12} : \frac{19}{6} = \frac{95}{12} \cdot \frac{6}{19} = \frac{95 \cdot 6}{12 \cdot 19} = \frac{19 \cdot 5 \cdot 6}{6 \cdot 2 \cdot 19} = \frac{5}{2} = 2 \frac{1}{2} $$

Ответ: e) $$\frac{68}{77}$$, ж) $$\frac{1}{15}$$, з) 4, и) $$1 \frac{1}{35}$$, к) $$\frac{27}{128}$$, л) $$2 \frac{1}{2}$$