1. **Problem statement:** Find the general term formula $b_n$ of a geometric progression satisfying the condition $b_4 + b_2 = 20$. 2. **Recall the general term of a geometric progression:** $$b_n = b_1 q^{n-1}$$ where $b_1$ is the first term and $q$ is the common ratio. 3. **Express the given condition using the formula:** $$b_4 + b_2 = b_1 q^{3} + b_1 q = b_1 (q^3 + q) = 20$$ 4. **Rewrite the equation:** $$b_1 (q^3 + q) = 20$$ 5. **We have one equation with two unknowns $b_1$ and $q$. To find the general term, we need more information or assumptions.** Since the problem only asks for the formula satisfying this condition, express $b_1$ in terms of $q$: $$b_1 = \frac{20}{q^3 + q}$$ 6. **Therefore, the general term is:** $$b_n = b_1 q^{n-1} = \frac{20}{q^3 + q} q^{n-1} = \frac{20 q^{n-1}}{q^3 + q}$$ This formula gives the general term $b_n$ of the geometric progression satisfying $b_4 + b_2 = 20$ for any $q \neq 0$ such that $q^3 + q \neq 0$. **Final answer:** $$b_n = \frac{20 q^{n-1}}{q^3 + q}$$