$a)\frac{2}{3}\cdot \frac{4}{5}+\frac{2}{3}\cdot \frac{2}{5}+\frac{2}{3}\cdot 0,6=\frac{2}{3}\cdot \left(\frac{4}{5}+\frac{2}{5}+0,6\right)=\frac{2}{3}\cdot \left(\frac{6}{5}+\frac{3}{5}\right)=\frac{2}{{\sout{3}}^1}\cdot \frac{{\sout{9}}^3}{5}=\frac{6}{5}=1\frac{1}{5}$

$b)\frac{1}{2}\cdot \frac{6}{7}-0,5\cdot \frac{3}{7}-\frac{2}{7}\cdot \frac{2}{4}=\frac{1}{2}\cdot \frac{6}{7}-\frac{1}{2}\cdot \frac{3}{7}-\frac{2}{7}\cdot \frac{1}{2}=\frac{1}{2}\cdot \left(\frac{6}{7}-\frac{3}{7}-\frac{2}{7}\right)=\frac{1}{2}\cdot \frac{1}{7}=\frac{1}{14}$