1: $\frac{2}{5}$ .$\frac{1}{6}$+ $\frac{2}{5}$. $\frac{2}{3}$ =$\frac{2}{5}$. ($\frac{1}{6}$+ $\frac{2}{3}$) =$\frac{2}{5}$. $\frac{5}{6}$=$\frac{1}{3}$ b:($\frac{-4}{15}$-$\frac{18}{19}$)-($\frac{20}{19}$ +$\frac{11}{15}$) =($\frac{-4}{15}$- $\frac{11}{15}$)- ($\frac{18}{19}$+ $\frac{20}{19}$)=-1+2=1