№3 а) \(\frac{5}{9} : \frac{10}{27}\); б) \(\frac{7}{10} - \frac{3}{20}\); в) \(\frac{6}{25} \cdot \frac{5}{18}\); г) \(5 \frac{2}{7} - 2 \frac{4}{21}\)

Решение:

1. а) \( \frac{5}{9} \div \frac{10}{27} = \frac{5}{9} \times \frac{27}{10} = \frac{5 \times 27}{9 \times 10} = \frac{1 \times 3}{1 \times 2} = \frac{3}{2} \)
2. б) \( \frac{7}{10} - \frac{3}{20} = \frac{14}{20} - \frac{3}{20} = \frac{14 - 3}{20} = \frac{11}{20} \)
3. в) \( \frac{6}{25} \times \frac{5}{18} = \frac{6 \times 5}{25 \times 18} = \frac{1 \times 1}{5 \times 3} = \frac{1}{15} \)
4. г) \( 5 \frac{2}{7} - 2 \frac{4}{21} = \frac{37}{7} - \frac{46}{21} = \frac{37 \times 3}{21} - \frac{46}{21} = \frac{111 - 46}{21} = \frac{65}{21} = 3 \frac{2}{21} \)

Ответ: а) \(\frac{3}{2}\); б) \(\frac{11}{20}\); в) \(\frac{1}{15}\); г) \(3 \frac{2}{21}\).