2) 7 -9/20 - 5 17/30 ;

2) $$7 \frac{-9}{20} - 5 \frac{17}{30} = (7 - 5) + (\frac{-9}{20} - \frac{17}{30}) = 2 + (\frac{-9 \cdot 3}{20 \cdot 3} - \frac{17 \cdot 2}{30 \cdot 2}) = 2 + (\frac{-27}{60} - \frac{34}{60}) = 2 - \frac{61}{60} = 2 - 1 \frac{1}{60} = 1 \frac{60}{60} - 1 \frac{1}{60} = \frac{59}{60}$$

Ответ: $$\frac{59}{60}$$