Ответ: 17/21
Решение:
\[1 - \frac{4}{7} - \frac{16}{21} = \frac{21}{21} - \frac{4 \cdot 3}{7 \cdot 3} - \frac{16}{21} = \frac{21}{21} - \frac{12}{21} - \frac{16}{21} = \frac{21 - 12 - 16}{21} = \frac{-7}{21} = -\frac{1}{3}\]
Ответ: -1/3