\[\boxed{\mathbf{173}.}\]
\[1)\ b_{1} = 100;\ \ q = - 0,1:\]
\[b_{6} = b_{1} \cdot q^{5} = 100 \cdot ( - 0,1)^{5} =\]
\[= - 10^{2} \cdot \frac{1}{10^{5}} = - \frac{1}{1000} =\]
\[= - 0,001.\]
\[2)\ b_{1} = - 27;\ \ q = - 1:\]
\[b_{50} = - 27 \cdot ( - 1)^{49} = 27.\]