№2 1 1 —— - —— 18 21 ———— 5 —— 63

Решим пример №2 из Блока №2:

$$ \frac{\frac{1}{18} - \frac{1}{21}}{\frac{5}{63}} = \frac{\frac{1 \cdot 7}{18 \cdot 7} - \frac{1 \cdot 6}{21 \cdot 6}}{\frac{5}{63}} = \frac{\frac{7}{126} - \frac{6}{126}}{\frac{5}{63}} = \frac{\frac{7 - 6}{126}}{\frac{5}{63}} = \frac{\frac{1}{126}}{\frac{5}{63}} = \frac{1}{126} : \frac{5}{63} = \frac{1}{126} \cdot \frac{63}{5} = \frac{1 \cdot 63}{126 \cdot 5} = \frac{1}{2 \cdot 5} = \frac{1}{10} $$

Ответ: $$\frac{1}{10}$$