1. Выполните умножение: 1) 5/7 * 2/3; 2) 4/9 * 27/40; 3) 6/13 * 13/18; 4) 34/45 * 25/51.

Решение:

1. \( \frac{5}{7} \cdot \frac{2}{3} = \frac{5 \cdot 2}{7 \cdot 3} = \frac{10}{21} \)
2. \( \frac{4}{9} \cdot \frac{27}{40} = \frac{4 \cdot 27}{9 \cdot 40} = \frac{1 \cdot 3}{1 \cdot 10} = \frac{3}{10} \)
3. \( \frac{6}{13} \cdot \frac{13}{18} = \frac{6 \cdot 13}{13 \cdot 18} = \frac{6}{18} = \frac{1}{3} \)
4. \( \frac{34}{45} \cdot \frac{25}{51} = \frac{34 \cdot 25}{45 \cdot 51} = \frac{2 \cdot 5}{9 \cdot 3} = \frac{10}{27} \)

Ответ: 1) \( \frac{10}{21} \); 2) \( \frac{3}{10} \); 3) \( \frac{1}{3} \); 4) \( \frac{10}{27} \).