The least number among $\sqrt[3]{4}, \sqrt[4]{5}, \sqrt[4]{7}$ and $\sqrt[3]{8}$ is:

For $x \ne 0$,the value of ${\left( {\frac{{{x^l}}}{{{x^m}}}} \right)^{({l^2} + lm + {m^2})}} {\left( {\frac{{{x^m}}}{{{x^n}}}} \right)^{({m^2} + nm + {n^2})}} {\left( {\frac{{{x^n}}}{{{x^l}}}} \right)^{({n^2} + nl + {l^2})}}$ is:

If $a^{1/x} = b^{1/y} = c^{1/z}$ and $b^2 = ac$,then $x + z = $

The number of digits in the decimal expansion of $16^5 \times 5^{16}$ is

$\frac{\sqrt{5/2} + \sqrt{7 - 3\sqrt{5}}}{\sqrt{7/2} + \sqrt{16 - 5\sqrt{7}}} = $

$20^{2-3x^2} = (40\sqrt{5})^{3x^2-2}$,then $x$ is equal to