Ответ:

  1. \(\frac{a-b}{3}+\frac{b}{3}=\frac{a-b+b}{3}=\frac{a}{3}\).
  2. \(\frac{7a^2}{6}-\frac{a^2}{6}=\frac{6a^2}{6}=a^2\).
  3. \(\frac{y}{4}\cdot\frac{16}{y^2}=\frac{16y}{4y^2}=\frac{4}{y}\).
  4. \(\frac{m^2}{5}\cdot\frac{m}{10}=\frac{m^3}{50}\).

Ответ: 1) \(\frac{a}{3}\); 2) \(a^2\); 3) \(\frac{4}{y}\); 4) \(\frac{m^3}{50}\).