If the ratio of sums of “n” terms of two A'P's is 2n :n+1, then the ratio of 8^th terms is

$\begin{array}{l}\frac{{\mathrm{S}}_{\mathrm{n}}}{{{\mathrm{S}}_{\mathrm{n}}}^{\mathrm{\prime }}}=\frac{2\mathrm{a}+(\mathrm{n}-1)\mathrm{d}}{2{\mathrm{a}}^{\mathrm{\prime }}+(\mathrm{n}-1){\mathrm{d}}^{\mathrm{\prime }}}=\frac{2\mathrm{n}}{\mathrm{n}+1}\\ \frac{{\mathrm{T}}_8}{{{\mathrm{T}}_8}^{\mathrm{\prime }}}=\frac{\mathrm{a}+7\mathrm{d}}{{\mathrm{a}}^{\mathrm{\prime }}+7{\mathrm{d}}^{\mathrm{\prime }}}=\frac{2\mathrm{a}+14\mathrm{d}}{2{\mathrm{a}}^{\mathrm{\prime }}+14{\mathrm{d}}^{\mathrm{\prime }}}=\frac{2\mathrm{a}+(15-1)\mathrm{d}}{2{\mathrm{a}}^{\mathrm{\prime }}+(15-1){\mathrm{d}}^{\mathrm{\prime }}}\\ \Rightarrow n=15\\ \Rightarrow \frac{a+7d}{a\text{'}+7d\text{'}}=\frac{2n}{n+1}=\frac{30}{16}=\frac{15}{8}\end{array}$