45.2:1

45. $$2 : 1\frac{1}{31} = 2 : \frac{32}{31} = 2 \cdot \frac{31}{32} = \frac{2 \cdot 31}{32} = \frac{1 \cdot 31}{16} = \frac{31}{16} = 1\frac{15}{16}$$

Ответ: $$1\frac{15}{16}$$