\[2,5;\ \ \ b_{2};\ \ \ b_{3};\ \ \ 20.\]
\[b_{4} = b_{1}q^{3}\]
\[q^{3} = \frac{20}{2,5}\]
\[q^{3} = 8\ \]
\[q = 2.\]
\[b_{2} = 2,5 \cdot 2 = 5;\ \]
\[b_{3} = 5 \cdot 2 = 10.\]
\[Ответ:\ \ 5;\ \ 10.\]