\[1\frac{8}{17}\ :\left( \frac{12}{17} + 2\frac{7}{11} \right) =\]
\[= \frac{25}{17}\ :\left( \frac{12^{\backslash 11}}{17} + \frac{29^{\backslash 17}}{11} \right) =\]
\[= \frac{25}{17}\ :\frac{132 + 493}{187} = \frac{28 \cdot 187}{17 \cdot 625} =\]
\[= \frac{28 \cdot 11}{625} = \frac{308}{625} = 0,4928.\]