\[\frac{20^{10}}{5^{10} \cdot 4^{10}} = \frac{(5 \cdot 4)^{10}}{5^{10} \cdot 4^{10}} = \frac{5^{10} \cdot 4^{10}}{5^{10} \cdot 4^{10}} =\]
\[= 5^{10 - 10} \cdot 4^{10 - 10} = 5^{0} \cdot 4^{0} =\]
\[= 1 \cdot 1 = 1.\]