Ответ:

  1. а)
    1. \(\frac{4}{7}+\frac{1}{7}=\frac{5}{7}\);
    2. \(\frac{9}{23}+\frac{11}{23}=\frac{20}{23}\);
    3. \(\frac{17}{40}-\frac{7}{40}=\frac{10}{40}=\frac{1}{4}\).
  2. б)
    1. \(\frac{5}{19}+\frac{2}{19}=\frac{7}{19}\);
    2. \(\frac{2}{15}+\frac{7}{15}=\frac{9}{15}=\frac{3}{5}\);
    3. \(\frac{7}{24}-\frac{5}{24}=\frac{2}{24}=\frac{1}{12}\).

Ответ: а) \(\frac{5}{7};\ \frac{20}{23};\ \frac{1}{4}\). б) \(\frac{7}{19};\ \frac{3}{5};\ \frac{1}{12}\).