$(3\frac{4}{9}-1\frac{16}{21}):1\frac{11}{42}-1\frac{5}{7}:6=1\frac{1}{21}$
а) $3\frac{4}{9}-1\frac{16}{21}=3\frac{28}{63}-1\frac{48}{63}=2\frac{91}{63}-1\frac{48}{63}=1\frac{43}{63}$
б) $1\frac{43}{63}:1\frac{11}{42}=\frac{106}{63}:\frac{53}{42}=\frac{106}{63}\ast \frac{42}{53}=\frac{2}{3}\ast \frac{2}{1}=\frac{4}{3}=1\frac{1}{3}$
в) $1\frac{5}{7}:6=\frac{12}{7}\ast \frac{1}{6}=\frac{2}{7}\ast \frac{1}{1}=\frac{2}{7}$
г) $1\frac{1}{3}-\frac{2}{7}=1\frac{7}{21}-\frac{6}{21}=1\frac{1}{21}$

$(4\frac{2}{3}:3\frac{1}{2}-3\frac{1}{2}:4\frac{2}{3}):1\frac{17}{18}=\frac{3}{10}$
а) $4\frac{2}{3}:3\frac{1}{2}=\frac{14}{3}:\frac{7}{2}=\frac{14}{3}\ast \frac{2}{7}=\frac{2}{3}\ast \frac{2}{1}=\frac{4}{3}=1\frac{1}{3}$
б) $3\frac{1}{2}:4\frac{2}{3}=\frac{7}{2}:\frac{14}{3}=\frac{7}{2}\ast \frac{3}{14}=\frac{1}{2}\ast \frac{3}{2}=\frac{3}{4}$
в) $1\frac{1}{3}-\frac{3}{4}=1\frac{4}{12}-\frac{9}{12}=\frac{16}{12}-\frac{9}{12}=\frac{7}{12}$
г) $\frac{7}{12}:1\frac{17}{18}=\frac{7}{12}:\frac{35}{18}=\frac{7}{12}\ast \frac{18}{35}=\frac{1}{2}\ast \frac{3}{5}=\frac{3}{10}$