a) $$\frac{3}{5} \cdot \frac{4}{3} = \frac{3 \cdot 4}{5 \cdot 3} = \frac{\cancel{3} \cdot 4}{5 \cdot \cancel{3}} = \frac{4}{5}$$.
б) $$\frac{2}{5} \cdot \frac{9}{8} = \frac{2 \cdot 9}{5 \cdot 8} = \frac{\cancel{2} \cdot 9}{5 \cdot \cancel{2} \cdot 4} = \frac{9}{20}$$.
в) $$\frac{4}{11} \cdot 11 = \frac{4 \cdot 11}{11} = \frac{4 \cdot \cancel{11}}{\cancel{11}} = 4$$.
г) $$\frac{1}{8} \cdot \frac{16}{5} = \frac{1 \cdot 16}{8 \cdot 5} = \frac{1 \cdot \cancel{8} \cdot 2}{\cancel{8} \cdot 5} = \frac{2}{5}$$.
д) $$\frac{11}{20} \cdot 5 = \frac{11 \cdot 5}{20} = \frac{11 \cdot \cancel{5}}{4 \cdot \cancel{5}} = \frac{11}{4} = 2 \frac{3}{4}$$.
е) $$1 \cdot \frac{13}{7} = \frac{13}{7} = 1 \frac{6}{7}$$.
Ответ: а) 4/5; б) 9/20; в) 4; г) 2/5; д) 2 3/4; е) 1 6/7