12. 7/24 : 9/40.

$$ \frac{7}{24} : \frac{9}{40} = \frac{7}{24} \cdot \frac{40}{9} = \frac{7}{3 \cdot 8} \cdot \frac{5 \cdot 8}{9} = \frac{7 \cdot 5}{3 \cdot 9} = \frac{35}{27} = 1 \frac{8}{27} $$

Ответ: $$1 \frac{8}{27} $$