1 5 -- = 3 12

$$\frac{1}{3} - \frac{5}{12} = \frac{1 \cdot 4}{3 \cdot 4} - \frac{5}{12} = \frac{4}{12} - \frac{5}{12} = -\frac{1}{12}$$

Ответ: $$\frac{-1}{12}$$