$\sqrt{10} \times \sqrt{250} = ?$

$\frac{\sqrt{4375}}{\sqrt{7}} = ?$

$(2 \sqrt{392}-21)+(\sqrt{8}-7)^{2}=(?)^{2}$

If $a = \frac{\sqrt{5} + 1}{\sqrt{5} - 1}$ and $b = \frac{\sqrt{5} - 1}{\sqrt{5} + 1}$,then the value of $\frac{a^{2} + ab + b^{2}}{a^{2} - ab + b^{2}}$ is

$A$ general wishing to draw up his $16160$ men in the form of a solid square found that he had $31$ men over. The number of men in the front row is:

Given that $\sqrt{10} = 3.16$,what is the value of $\sqrt{\frac{4}{12.1}}$ to one place of decimal?