3 3/4 - 1 1/4=

$$3 \frac{3}{4} - 1 \frac{1}{4} = (3 - 1) + (\frac{3}{4} - \frac{1}{4}) = 2 + \frac{3 - 1}{4} = 2 + \frac{2}{4} = 2 + \frac{1}{2} = 2 \frac{1}{2}$$

Ответ: 2 1/2