\[\boxed{\mathbf{55}\mathbf{.}}\]
\[1)\ \sqrt{x^{3}} = \sqrt[2]{x^{3}} = x^{\frac{3}{2}} = x^{1\frac{1}{2}}\]
\[2)\ \sqrt[3]{a^{4}} = a^{\frac{4}{3}} = a^{1\frac{1}{3}}\]
\[3)\ \sqrt[4]{b^{3}} = b^{\frac{3}{4}}\]
\[4)\ \sqrt[5]{x^{- 1}} = x^{- \frac{1}{5}}\]
\[5)\ \sqrt[6]{a} = \sqrt[6]{a^{1}} = a^{\frac{1}{6}}\]
\[6)\ \sqrt[7]{b^{- 3}} = b^{- \frac{3}{7}}\]