10) 3 2/21 - 1 11/21 =

10) $$\begin{aligned}3\frac{2}{21} - 1\frac{11}{21} &= 2 + \frac{21}{21} + \frac{2}{21} - 1\frac{11}{21} = 2 + \frac{23}{21} - 1 - \frac{11}{21} = 1\frac{12}{21} = 1\frac{4}{7}\\\\&=\frac{1 \cdot 21 + 12}{21} = \frac{21+12}{21} = \frac{33}{21} = \frac{11}{7} = 1\frac{4}{7}\end{aligned}$$

Ответ: 1 4/7