\[\boxed{\mathbf{2.}\mathbf{356}}\]
\[\textbf{а)}\ \frac{1}{5} \cdot \frac{5}{6} = \frac{1}{6} \cdot \frac{6}{7} = \frac{1}{7} \cdot \frac{7}{8} =\]
\[= \frac{1}{8} \cdot \frac{8}{9} = \frac{1}{9}.\]
\[\textbf{б)}\frac{4}{15} \cdot 0 = 0\]
\[\frac{4}{15} \cdot 3 = \frac{4}{5}\]
\[\frac{4}{15} \cdot 4 = \frac{16}{15} = 1\frac{1}{15}\]
\[\frac{4}{15} \cdot 5 = \frac{4}{3} = 1\frac{1}{3}\]