612. Выполните действия: б) \frac{11}{12} : \frac{24}{25} \cdot \frac{21}{22};

$$\frac{11}{12} : \frac{24}{25} \cdot \frac{21}{22} = \frac{11}{12} \cdot \frac{25}{24} \cdot \frac{21}{22} = \frac{11}{12} \cdot \frac{25}{24} \cdot \frac{21}{2 \cdot 11} = \frac{1}{12} \cdot \frac{25}{24} \cdot \frac{21}{2} = \frac{1}{4 \cdot 3} \cdot \frac{25}{24} \cdot \frac{3 \cdot 7}{2} = \frac{1}{4} \cdot \frac{25}{24} \cdot \frac{7}{2} = \frac{175}{192}$$

Ответ: \frac{175}{192}