5. Вычислим:$$ 1 - \frac{4}{7} : \frac{16}{21} = 1 - \frac{4}{7} \cdot \frac{21}{16} = 1 - \frac{4 \cdot 21}{7 \cdot 16} = 1 - \frac{84}{112} = 1 - \frac{3}{4} = \frac{4}{4} - \frac{3}{4} = \frac{1}{4} $$
Ответ: $$\frac{1}{4}$$