$\frac{? \div 12}{0.2 \times 3.6} = 2$

If $x = \frac{4 \sqrt{ab}}{\sqrt{a} + \sqrt{b}}$,then what is the value of $\frac{x + 2 \sqrt{a}}{x - 2 \sqrt{a}} + \frac{x + 2 \sqrt{b}}{x - 2 \sqrt{b}}$ (when $a \neq b$)?

Eight persons are planning to share equally the rent of a car. If one person withdraws from the arrangement and the others share equally the entire cost of the car,then the share of each of the remaining persons increases by what fraction?

$A$ printer numbers the pages of a book starting with $1$ and uses $3189$ digits in all. How many pages does the book have?

The least number that must be subtracted from $63520$ to make the result a perfect square is

If $\frac{\sqrt{5+x}+\sqrt{5-x}}{\sqrt{5+x}-\sqrt{5-x}}=3,$ then what is the value of $x?$