4/ 10³ (2⁴)⁵

4) $$ \frac{10^3 \cdot (2^4)^5}{5^3 \cdot 8^{21}} = \frac{10^3 \cdot 2^{20}}{5^3 \cdot (2^3)^{21}} = \frac{(2 \cdot 5)^3 \cdot 2^{20}}{5^3 \cdot 2^{63}} = \frac{2^3 \cdot 5^3 \cdot 2^{20}}{5^3 \cdot 2^{63}} = \frac{2^{23}}{2^{63}} = \frac{1}{2^{40}} $$

Ответ: $$\frac{1}{2^{40}}$$