Simplify:
$\frac{3}{10} \div \frac{3}{7} \text{ of } \left(2 \frac{3}{10} + 2 \frac{3}{5}\right) + \frac{1}{5} \div 1 \frac{2}{5} - \frac{2}{7}$

If $a^{4}+a^{2} b^{2}+b^{4}=8$ and $a^{2}+a b+b^{2}=4,$ then the value of $a b$ is

The value of $\left\{\left(\sqrt[n]{x^{2}}\right)^{n / 2}\right\}^{2}$ is

Find the value of the following expression up to four places of decimals:
$\left[1+\frac{1}{1 \times 2}+\frac{1}{1 \times 2 \times 4}+\frac{1}{1 \times 2 \times 4 \times 8}+\frac{1}{1 \times 2 \times 4 \times 8 \times 16}\right]$

What approximate value will come in place of the question mark $(?)$ in the given equation? (You are not expected to calculate the exact value)
$\frac{7702}{43.96} + 25.11 \times 45.88 = ? \times 15$

If $\sqrt{1+\frac{x}{144}}=\frac{13}{12},$ then $x$ equals to