8. Выполнить деление:

Решение:

1. \( 4 \div \frac{8}{9} = 4 \cdot \frac{9}{8} = \frac{4 \cdot 9}{8} = \frac{36}{8} = \frac{9}{2} = 4 \frac{1}{2} \)
2. \( \frac{12}{21} \div 6 = \frac{12}{21} \cdot \frac{1}{6} = \frac{12}{21 \cdot 6} = \frac{12}{126} = \frac{2}{21} \)
3. \( \frac{14}{15} \div \frac{4}{35} = \frac{14}{15} \cdot \frac{35}{4} = \frac{14 \cdot 35}{15 \cdot 4} = \frac{(2 \cdot 7) \cdot (5 \cdot 7)}{(3 \cdot 5) \cdot (2 \cdot 2)} = \frac{7 \cdot 7}{3 \cdot 2} = \frac{49}{6} = 8 \frac{1}{6} \)
4. \( 1 \frac{1}{4} \div \frac{3}{8} = \frac{5}{4} \cdot \frac{8}{3} = \frac{5 \cdot 8}{4 \cdot 3} = \frac{40}{12} = \frac{10}{3} = 3 \frac{1}{3} \)
5. \( 3 \frac{2}{5} \div 1 \frac{7}{10} = \frac{17}{5} \div \frac{17}{10} = \frac{17}{5} \cdot \frac{10}{17} = \frac{17 \cdot 10}{5 \cdot 17} = \frac{10}{5} = 2 \)
6. \( \frac{5}{16} \div 3 \frac{1}{8} = \frac{5}{16} \div \frac{25}{8} = \frac{5}{16} \cdot \frac{8}{25} = \frac{5 \cdot 8}{16 \cdot 25} = \frac{40}{400} = \frac{1}{10} \)

Ответ: 8-а) \( 4 \frac{1}{2} \), 8-б) \( \frac{2}{21} \), 8-в) \( 8 \frac{1}{6} \), 8-г) \( 3 \frac{1}{3} \), 8-д) \( 2 \), 8-е) \( \frac{1}{10} \).