1) a) $$20a^3 \cdot (5a)^2 = 20a^3 \cdot 25a^2 = 500a^5$$.
б) $$-0,4x^5 \cdot (2x^3)^4 = -0,4x^5 \cdot 16x^{12} = -6,4x^{17}$$.
Ответ: $$500a^5; -6,4x^{17}$$