б) Вычислите: (\frac{4}{5}-\frac{8}{15})\cdot\frac{5}{12}

Вычисляем: \[\left(\frac{4}{5} - \frac{8}{15}\right) \cdot \frac{5}{12} = \left(\frac{4\cdot3}{5\cdot3} - \frac{8}{15}\right) \cdot \frac{5}{12} = \left(\frac{12}{15} - \frac{8}{15}\right) \cdot \frac{5}{12} = \frac{4}{15} \cdot \frac{5}{12} = \frac{4\cdot5}{15\cdot12} = \frac{20}{180} = \frac{1}{9}\]

Ответ: \(\frac{1}{9}\)