What is the difference between the biggest and the smallest fraction among $\frac{2}{3}, \frac{3}{4}, \frac{4}{5}$ and $\frac{5}{6}$?

$\left\{7 \frac{1}{2} + \frac{1}{2} \div \frac{1}{2} \text{ of } \frac{1}{4} - \frac{2}{5} \times 2 \frac{1}{3} \div 1 \frac{7}{8} \text{ of } \left(1 \frac{2}{5} - 1 \frac{1}{3}\right)\right\} = ?$

If $x^{2}+y^{2}+z^{2}+2=2(y-x)$,then the value of $x^{3}+y^{3}+z^{3}$ is equal to

The value of $\frac{1}{1 \times 2} + \frac{1}{2 \times 3} + \frac{1}{3 \times 4} + \ldots + \frac{1}{9 \times 10}$ is

When simplified,the value of the product $\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right) \ldots\left(1-\frac{1}{n}\right)$ equals

$2+\sqrt{2}+\frac{1}{2+\sqrt{2}}+\frac{1}{\sqrt{2}-2}=?$