3) 40.(-13.

3) $$40 \cdot (\frac{1}{2})^2 - 13 \cdot \frac{1}{8} = 40 \cdot \frac{1}{4} - \frac{13}{8} = 10 - \frac{13}{8} = \frac{10 \cdot 8}{8} - \frac{13}{8} = \frac{80}{8} - \frac{13}{8} = \frac{67}{8} = 8,375$$

Ответ: 8,375