1. Вычислить: 1)-1,8-15; 2)-6,9-2,3; 3)-3-(-8)-5; 4)-2$$\frac{4}{5}$$\cdot$$\frac{5}{7}$$; 5) 2$$\frac{3}{7}$$ + $$\frac{1}{6}$$

-1,8 - 15 = -16,8

-6,9 - 2,3 = -9,2

-3 - (-8) - 5 = -3 + 8 - 5 = 5 - 5 = 0

-2$$\frac{4}{5}$$\cdot$$\frac{5}{7}$$ = -$$\frac{14}{5}$$\cdot$$\frac{5}{7}$$ = -$$\frac{14 \cdot 5}{5 \cdot 7}$$ = -$$\frac{2 \cdot 7 \cdot 5}{5 \cdot 7}$$ = -2

2$$\frac{3}{7}$$ + $$\frac{1}{6}$$ = $$\frac{17}{7}$$ + $$\frac{1}{6}$$ = $$\frac{17 \cdot 6}{7 \cdot 6}$$ + $$\frac{1 \cdot 7}{6 \cdot 7}$$ = $$\frac{102}{42}$$ + $$\frac{7}{42}$$ = $$\frac{102 + 7}{42}$$ = $$\frac{109}{42}$$ = 2$$\frac{25}{42}$$