7) 2 5/12+(-17 3/8);

7) $$2 \frac{5}{12} + (-17 \frac{3}{8}) = 2 \frac{5}{12} - 17 \frac{3}{8} = \frac{29}{12} - \frac{139}{8} = \frac{29 \cdot 2}{12 \cdot 2} - \frac{139 \cdot 3}{8 \cdot 3} = \frac{58}{24} - \frac{417}{24} = \frac{58 - 417}{24} = \frac{-359}{24} = -14 \frac{23}{24}$$

Ответ: $$-14 \frac{23}{24}$$