9. Обчисли: 1) 2/5 * 4/7; 2) 1/3 * 3/5; 3) 4/9 * 5/12; 5) 13/15 * 1/26; 6) 1/8 * 8/9; 7) 3/5 * 5/3; 9) 5 * 1/3; 10) 4/13 * 3; 11) 5/21 * 3

**Ответы:** 1) $$\frac{2}{5} \cdot \frac{4}{7} = \frac{2 \cdot 4}{5 \cdot 7} = \frac{8}{35}$$ 2) $$\frac{1}{3} \cdot \frac{3}{5} = \frac{1 \cdot \cancel{3}^1}{\cancel{3}_1 \cdot 5} = \frac{1}{5}$$ 3) $$\frac{4}{9} \cdot \frac{5}{12} = \frac{\cancel{4}^1 \cdot 5}{9 \cdot \cancel{12}_3} = \frac{5}{27}$$ 5) $$\frac{13}{15} \cdot \frac{1}{26} = \frac{\cancel{13}^1 \cdot 1}{15 \cdot \cancel{26}_2} = \frac{1}{30}$$ 6) $$\frac{1}{8} \cdot \frac{8}{9} = \frac{1 \cdot \cancel{8}^1}{\cancel{8}_1 \cdot 9} = \frac{1}{9}$$ 7) $$\frac{3}{5} \cdot \frac{5}{3} = \frac{\cancel{3}^1 \cdot \cancel{5}^1}{\cancel{5}_1 \cdot \cancel{3}_1} = 1$$ 9) $$5 \cdot \frac{1}{3} = \frac{5 \cdot 1}{3} = \frac{5}{3} = 1\frac{2}{3}$$ 10) $$\frac{4}{13} \cdot 3 = \frac{4 \cdot 3}{13} = \frac{12}{13}$$ 11) $$\frac{5}{21} \cdot 3 = \frac{5 \cdot \cancel{3}^1}{\cancel{21}_7} = \frac{5}{7}$$