Fill in the blanks to make the following statement true: $\sqrt{49} = \ldots \ldots$

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

Rationalise the denominator of the following expression and evaluate it by taking $\sqrt{2}=1.414, \sqrt{3}=1.732$,and $\sqrt{5}=2.236$ up to three decimal places:
$\frac{\sqrt{2}}{2+\sqrt{2}}$

Find the value of $a$ :
$\frac{3-\sqrt{5}}{3+2 \sqrt{5}}=a \sqrt{5}-\frac{19}{11}$

Rationalise the denominator in each of the following:
$\frac{18}{3 \sqrt{2}-2 \sqrt{3}}$

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.
$\frac{6}{\sqrt{6}}$