Ответ:

  1. а) \(\frac{3}{4}=\frac{6}{8}\), поэтому \(\frac{6}{8}+\frac{1}{8}=\frac{7}{8}\).
  2. б) Общий знаменатель — 60: \(\frac{11}{15}-\frac{7}{20}=\frac{44}{60}-\frac{21}{60}=\frac{23}{60}\).
  3. в) \(\frac{5}{4}\cdot\frac{2}{3}=\frac{10}{12}=\frac{5}{6}\).
  4. г) \(\frac{3}{20}:\frac{9}{10}=\frac{3}{20}\cdot\frac{10}{9}=\frac{1}{6}\).
  5. д) \(2\frac{2}{5}+3\frac{1}{6}=5+\frac{2}{5}+\frac{1}{6}=5+\frac{12}{30}+\frac{5}{30}=5\frac{17}{30}\).
  6. ж) \(4\frac{2}{15}\cdot5=\frac{62}{15}\cdot5=\frac{62}{3}=20\frac{2}{3}\).
  7. з) \(7\frac{3}{5}:19=\frac{38}{5}:19=\frac{38}{5}\cdot\frac{1}{19}=\frac{2}{5}\).

Ответ: а) \(\frac{7}{8}\); б) \(\frac{23}{60}\); в) \(\frac{5}{6}\); г) \(\frac{1}{6}\); д) \(5\frac{17}{30}\); ж) \(20\frac{2}{3}\); з) \(\frac{2}{5}\).