81. Найдите значение выражения: а) \((\frac{3}{5}-\frac{4}{15})\cdot(\frac{1}{2}-\frac{1}{3})\); б) \(10-5\cdot1\frac{1}{5}-\frac{1}{3}\); в) \(\frac{\frac{1}{2}+\frac{3}{4}}{\frac{1}{2}}\); г) \(\frac{\frac{7}{10}+\frac{3}{5}}{\frac{7}{10}+\frac{1}{2}}\).

а) \(\left(\frac{3}{5}-\frac{4}{15}\right)\cdot\left(\frac{1}{2}-\frac{1}{3}\right)=\left(\frac{9}{15}-\frac{4}{15}\right)\cdot\frac{1}{6}=\frac{1}{3}\cdot\frac{1}{6}=\frac{1}{18}\).

б) \(10-5\cdot1\frac{1}{5}-\frac{1}{3}=10-5\cdot\frac{6}{5}-\frac{1}{3}=10-6-\frac{1}{3}=\frac{11}{3}\).

в) \(\frac{\frac{1}{2}+\frac{3}{4}}{\frac{1}{2}}=\frac{\frac{2}{4}+\frac{3}{4}}{\frac{1}{2}}=\frac{5}{4}\cdot2=\frac{5}{2}\).

г) \(\frac{\frac{7}{10}+\frac{3}{5}}{\frac{7}{10}+\frac{1}{2}}=\frac{\frac{7}{10}+\frac{6}{10}}{\frac{7}{10}+\frac{5}{10}}=\frac{\frac{13}{10}}{\frac{12}{10}}=\frac{13}{12}\).

Ответ: а) \(\frac{1}{18}\); б) \(\frac{11}{3}\); в) \(\frac{5}{2}\); г) \(\frac{13}{12}\).