$\sqrt{10} \times \sqrt{15}$ is equal to

Rationalise the denominator of the following:
$\frac{2+\sqrt{3}}{2-\sqrt{3}}$

Rationalise the denominator in each of the following and hence evaluate by taking $\sqrt{2}=1.414, \sqrt{3}=1.732$ and $\sqrt{5}=2.236,$ up to three places of decimal.
$\frac{6}{\sqrt{6}}$

Multiply $5 \sqrt{3}$ and $4 \sqrt{12}$.

Find three rational numbers between $\frac{2}{3}$ and $\frac{4}{5}$.

If $\sqrt{2} = 1.4142$,then $\sqrt{\frac{\sqrt{2}-1}{\sqrt{2}+1}}$ is equal to