a) $A=\left[\frac{2}{7}\left(\frac{1}{4}-\frac{1}{3}\right)\right]:\left[\frac{2}{7}\left(\frac{1}{3}-\frac{2}{5}\right)\right]=\left(\frac{1}{4}-\frac{1}{3}\right):\left(\frac{1}{3}-\frac{2}{5}\right)=1\frac{1}{4}$.
b) $B=\frac{\frac{3}{4}\left(\frac{1}{5}-\frac{2}{7}-\frac{1}{3}+\frac{2}{7}\right)}{\frac{1}{5}\left(\frac{2}{7}+\frac{1}{3}\right)-\frac{1}{3}\left(\frac{2}{7}+\frac{1}{3}\right)}=\frac{\frac{3}{4}\left(\frac{1}{5}-\frac{1}{3}\right)}{\left(\frac{1}{5}-\frac{1}{3}\right)\left(\frac{2}{7}+\frac{1}{3}\right)}=1\frac{11}{52}$.

a) $A=\frac{3}{5}.\frac{6}{7}+\frac{3}{7}.\frac{3}{5}-\frac{2}{7}.\frac{3}{5}$
$=\frac{3}{5}\cdot \left(\frac{6}{7}+\frac{3}{7}-\frac{2}{7}\right)=\frac{3}{5}$
b) $B=\left(-13\cdot \frac{2}{5}+\frac{-2}{9}\cdot \frac{2}{5}+\frac{2}{5}\cdot \frac{11}{9}\right)\cdot \frac{5}{2}$
$=\left(-13-\frac{2}{9}+\frac{11}{9}\right)\cdot \frac{2}{5}\cdot \frac{5}{2}=-13+\left(\frac{11}{9}-\frac{2}{9}\right)=-12.$
c) $C=\left(\frac{-4}{5}+\frac{5}{7}\right)\cdot \frac{3}{2}+\left(\frac{-1}{5}+\frac{2}{7}\right)\cdot \frac{3}{2}=\left(\frac{-4}{5}+\frac{5}{7}+\frac{-1}{5}+\frac{2}{7}\right)\cdot \frac{3}{2}=\left(\left(\frac{-4}{5}+\frac{-1}{5}\right)+\left(\frac{5}{7}+\frac{2}{7}\right)\right)\cdot \frac{3}{2}=0.$
d) $D=\frac{4}{9}:\left(\frac{1}{15}-\frac{10}{15}\right)+\frac{4}{9}:\left(\frac{2}{22}-\frac{5}{22}\right)$
$=\frac{4}{9}:\frac{-3}{5}+\frac{4}{9}:\frac{-3}{22}=\frac{4}{9}\cdot \frac{-5}{3}+\frac{4}{9}.\frac{-22}{3}$
$=\frac{4}{9}\cdot \left(\frac{-5}{3}+\frac{-22}{3}\right)=\frac{4}{9}.\frac{-27}{3}=-4.$

a) $A=\left(\frac{1}{3}+\frac{2}{3}\right)-\left(\frac{8}{15}+\frac{7}{15}\right)+\left(\frac{-1}{7}+1\frac{1}{7}\right)=1-1+1=1$;
b) $B=\left(0.25-1\frac{1}{4}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)-\frac{1}{8}$
$=\left(\frac{1}{4}-1-\frac{1}{4}\right)+1-\frac{1}{8}=\frac{-1}{8}$.

a) $P=\frac{2}{3}+\frac{1}{4}+\frac{3}{5}-\frac{7}{45}+\frac{5}{9}+\frac{1}{12}+\frac{1}{35}$ $=\left(\frac{2}{3}+\frac{1}{4}+\frac{1}{12}\right)+\left(\frac{5}{9}-\frac{7}{45}\right)+\frac{3}{5}+\frac{1}{35}=1+\frac{4}{5}+\frac{3}{5}+\frac{1}{35}=2\frac{1}{35}$