Ответ:

  1. \(3\frac{5}{8}+1\frac{2}{3}=\frac{29}{8}+\frac{5}{3}=\frac{87}{24}+\frac{40}{24}=\frac{127}{24}=5\frac{7}{24}\).

  2. \(4\frac{4}{9}-2\frac{5}{6}=\frac{40}{9}-\frac{17}{6}=\frac{80}{18}-\frac{51}{18}=\frac{29}{18}=1\frac{11}{18}\).

  3. \(6\frac{7}{12}+\left(5\frac{3}{40}-4\frac{8}{15}\right)\)

    \(=6\frac{7}{12}+\left(\frac{603}{120}-\frac{568}{120}\right)=6\frac{7}{12}+\frac{7}{24}=6\frac{14}{24}+\frac{7}{24}=6\frac{7}{8}\).

Ответ: а) \(5\frac{7}{24}\); б) \(1\frac{11}{18}\); в) \(6\frac{7}{8}\).