№3 a) 5/9 ÷ 10/27; б) 7/10 - 3/20; в) 6/25 • 5/18; г) 5 2/7 - 2 4/21 + 3 2/3.

Решение:

1. а) \( \frac{5}{9} \div \frac{10}{27} = \frac{5}{9} \times \frac{27}{10} = \frac{5 \times 27}{9 \times 10} = \frac{1 \times 3}{1 \times 2} = \frac{3}{2} = 1\frac{1}{2} \)
2. б) \( \frac{7}{10} - \frac{3}{20} = \frac{14}{20} - \frac{3}{20} = \frac{11}{20} \)
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) \( 5\frac{2}{7} - 2\frac{4}{21} + 3\frac{2}{3} = \frac{37}{7} - \frac{46}{21} + \frac{11}{3} = \frac{111}{21} - \frac{46}{21} + \frac{77}{21} = \frac{111 - 46 + 77}{21} = \frac{142}{21} = 6\frac{16}{21} \)

Ответ: а) 1 1/2; б) 11/20; в) 1/15; г) 6 16/21.