Let's rationalize the denominators of the following fractions:
a) $\frac{1}{\sqrt{2}+\sqrt{3}-\sqrt{5}}$,
b) $\frac{\sqrt{a+x}+\sqrt{a-x}}{\sqrt{a+x}-\sqrt{a-x}}$
$$
\begin{aligned}
& \text { (a) } \frac{1}{\sqrt{2}+\sqrt{3}-\sqrt{5}}=\frac{\sqrt{2}+\sqrt{3}+\sqrt{5}}{2 \sqrt{6}}=\frac{2 \sqrt{3}+3 \sqrt{2}+\sqrt{30}}{12} \\
& \text { (b) } \frac{\sqrt{a+x}+\sqrt{a-x}}{\sqrt{a+x}-\sqrt{a-x}}=\frac{\left(\sqrt{a+x}+\sqrt{(a-x)^{2}}\right)}{a+x-(a-x)}=\frac{a+\sqrt{a^{2}-x^{2}}}{x}
\end{aligned}
$$

(Rudolf Szabó, Eger.)

Number of solutions: 36.