If $4^{\text {th }}, 10^{\text {th }}$ and $16^{\text {th }}$ terms of a G.P. are $x, y$ and $z$ respectively, then

If $S_n$ stands for sum to $n$-terms of a GP with $a$ as the first term and $r$ as the common ratio, then $S_n: S_{2 n}$ is

If $$p\left(\frac{1}{q}+\frac{1}{r}\right), q\left(\frac{1}{r}+\frac{1}{p}\right), r\left(\frac{1}{p}+\frac{1}{q}\right)$$ are in $$\mathrm{AP}$$, then $$p, q, r$$

$$n$$th term of the series $$1+\frac{3}{7}+\frac{5}{7^2}+\frac{1}{7^2}+\ldots$$ is