\[\sqrt[4]{x\sqrt[5]{x}} = \sqrt[4]{\sqrt[5]{x^{5}} \cdot \sqrt[5]{x}} =\]
\[= \sqrt[4]{\sqrt[5]{x^{5} \cdot x}} = \sqrt[4]{\sqrt[5]{x^{6}}} =\]
\[= \sqrt[20]{x^{6}} = \sqrt[10]{x^{3}}\]
\[x = \sqrt[3]{5^{10}}:\]
\[\sqrt[10]{\left( \sqrt[3]{5^{10}} \right)^{3}} = \sqrt[10]{5^{10}} = 5.\]