Решение примеров:

3)

$$\frac{3}{5} \cdot \frac{25}{4} = \frac{3 \cdot 25}{5 \cdot 4} = \frac{3 \cdot 5 \cdot 5}{5 \cdot 4} = \frac{3 \cdot 5}{4} = \frac{15}{4} = 3\frac{3}{4}$$

4)

$$\frac{9}{5} \cdot \frac{2}{3} = \frac{9 \cdot 2}{5 \cdot 3} = \frac{3 \cdot 3 \cdot 2}{5 \cdot 3} = \frac{3 \cdot 2}{5} = \frac{6}{5} = 1\frac{1}{5}$$

5)

$$\frac{5}{3} \cdot \frac{9}{2} = \frac{5 \cdot 9}{3 \cdot 2} = \frac{5 \cdot 3 \cdot 3}{3 \cdot 2} = \frac{5 \cdot 3}{2} = \frac{15}{2} = 7\frac{1}{2}$$

6)

$$\frac{7}{5} \cdot \frac{12}{35} = \frac{7 \cdot 12}{5 \cdot 35} = \frac{7 \cdot 12}{5 \cdot 7 \cdot 5} = \frac{12}{5 \cdot 5} = \frac{12}{25}$$

9)

$$\frac{3}{5} \cdot \frac{4}{35} = \frac{3 \cdot 4}{5 \cdot 35} = \frac{12}{175}$$

10)

$$\frac{15}{4} \cdot \frac{3}{7} = \frac{15 \cdot 3}{4 \cdot 7} = \frac{45}{28} = 1\frac{17}{28}$$

11)

$$\frac{21}{2} \cdot \frac{3}{5} = \frac{21 \cdot 3}{2 \cdot 5} = \frac{63}{10} = 6\frac{3}{10}$$

12)

$$\frac{14}{5} \cdot \frac{7}{2} = \frac{14 \cdot 7}{5 \cdot 2} = \frac{7 \cdot 2 \cdot 7}{5 \cdot 2} = \frac{7 \cdot 7}{5} = \frac{49}{5} = 9\frac{4}{5}$$