№3 1 1 —— - —— 35 60 ———— 1 — 21

Решим пример №3 из Блока №2:

$$ \frac{\frac{1}{35} - \frac{1}{60}}{\frac{1}{21}} = \frac{\frac{1 \cdot 12}{35 \cdot 12} - \frac{1 \cdot 7}{60 \cdot 7}}{\frac{1}{21}} = \frac{\frac{12}{420} - \frac{7}{420}}{\frac{1}{21}} = \frac{\frac{12 - 7}{420}}{\frac{1}{21}} = \frac{\frac{5}{420}}{\frac{1}{21}} = \frac{5}{420} : \frac{1}{21} = \frac{5}{420} \cdot \frac{21}{1} = \frac{5 \cdot 21}{420 \cdot 1} = \frac{5}{20} = \frac{1}{4} $$

Ответ: $$\frac{1}{4}$$