1) -1,8 * 15 = -27
2) -6,9 - 2,3 = -9,2
3) -3 - (-8) - 5 = -3 + 8 - 5 = 5 - 5 = 0
4) -2$$\frac{4}{7}$$ : $$\frac{5}{7}$$ = -$$\frac{18}{7}$$ : $$\frac{5}{7}$$ = -$$\frac{18}{7}$$ * $$\frac{7}{5}$$ = -$$\frac{18}{5}$$ = -3$$\frac{3}{5}$$ = -3,6
5) 2$$\frac{3}{7}$$ + $$\frac{1}{6}$$ = $$\frac{17}{7}$$ + $$\frac{1}{6}$$ = $$\frac{17*6}{7*6}$$ + $$\frac{1*7}{6*7}$$ = $$\frac{102}{42}$$ + $$\frac{7}{42}$$ = $$\frac{109}{42}$$ = 2$$\frac{25}{42}$$