\[\boxed{\text{111.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
Пояснение.
Решение.
\[\textbf{а)}\ \frac{3x}{4y} \cdot \frac{10}{3x^{2}} = \frac{3x \cdot 10}{4y \cdot 3x²} = \frac{5}{2xy}\]
\[\textbf{б)}\ \frac{2,5}{2a^{2}} \cdot \frac{4a^{3}}{5b^{2}} = \frac{2,5 \cdot 4a³}{2a^{2} \cdot 5b²} = \frac{a}{b^{2}}\]
\[\textbf{в)}\ \frac{7a^{3}}{24b} \cdot 8b^{2} = \frac{7a^{3} \cdot 8b^{2}}{24b} = \frac{7a^{3}b}{3}\]
\[\textbf{г)}\ 14\ ab \cdot \frac{1}{21b^{3}} = \frac{14ab}{21b^{3}} = \frac{2a}{3b^{2}}\]
\[\text{\ }\]