12) 10 3/8 - 2 5/8 =

12) $$\begin{aligned}10\frac{3}{8} - 2\frac{5}{8} &= 9 + \frac{8}{8} + \frac{3}{8} - 2\frac{5}{8} = 9 + \frac{11}{8} - 2 - \frac{5}{8} = 7\frac{6}{8} = 7\frac{3}{4}\\\\&=\frac{7 \cdot 8 + 6}{8} = \frac{56+6}{8} = \frac{62}{8} = \frac{31}{4} = 7\frac{3}{4}\end{aligned}$$

Ответ: 7 3/4