1) $\frac{-2}{5}$ : (1-$\frac{1}{10}$)
= $\frac{-5}{2}$ × (1-$\frac{1}{10}$)
= $\frac{-5}{2}$ + $\frac{5}{20}$
= $\frac{-50}{20}$ + $\frac{5}{20}$
= $\frac{-45}{50}$=$\frac{-9}{10}$
2) $\frac{-5}{11}$ + ( $\frac{-6}{11}$ + 1)
= $\frac{-5}{11}$ + $\frac{-6}{11}$ + 1
= $\frac{-5-6}{11}$ + 1
= $\frac{-11}{11}$ + 1 = -1+1=0
3) $\frac{2}{3}$ + ($\frac{5}{7}$ + $\frac{-2}{3}$)
= $\frac{2}{3}$ + $\frac{5}{7}$ + $\frac{-2}{3}$
= $\frac{5}{7}$
4) ( $\frac{-1}{4}$ + $\frac{5}{8}$ ) + $\frac{-3}{8}$
= $\frac{-1}{4}$ + $\frac{5}{8}$ + $\frac{-3}{8}$
= $\frac{-1}{4}$ + $\frac{2}{8}$
= $\frac{-1}{4}$ + $\frac{1}{4}$ = 0
