6 3/8 : 25 1/2 =

$$ 6\frac{3}{8} : 25\frac{1}{2} = \frac{51}{8} : \frac{51}{2} = \frac{51}{8} \cdot \frac{2}{51} = \frac{1}{4} $$

Ответ: $$\frac{1}{4}$$