Решение:

• б) $$rac{25}{16y^2} \cdot 2y^2 = \frac{25 \cdot 2y^2}{16y^2} = \frac{50y^2}{16y^2} = \frac{25}{8} = 3\frac{1}{8}$$
• в) $$6am^2 \cdot \frac{4a}{3m^3} = \frac{6am^2 \cdot 4a}{3m^3} = \frac{24a^2m^2}{3m^3} = \frac{8a^2}{m}$$
• в) $$\frac{72x^4}{25y^5} \cdot (-\frac{2.5y^4}{27x^5}) = -\frac{72x^4 \cdot 2.5y^4}{25y^5 \cdot 27x^5} = -\frac{72 \cdot 2.5}{25 \cdot 27} \cdot \frac{x^4}{x^5} \cdot \frac{y^4}{y^5} = -\frac{8 \cdot 1}{10 \cdot 3} \cdot \frac{1}{x} \cdot \frac{1}{y} = -\frac{4}{15xy}$$
• г) $$\frac{35ax^2}{12b^2y} \cdot \frac{8ab}{21xy} = \frac{35ax^2 \cdot 8ab}{12b^2y \cdot 21xy} = \frac{35 \cdot 8}{12 \cdot 21} \cdot \frac{a^2x^2b}{b^2xy^2} = \frac{5 \cdot 2}{3 \cdot 3} \cdot \frac{a^2x}{bxy^2} = \frac{10a^2x}{9bxy^2} = \frac{10a^2}{9by^2}$$