SSC CHSL 6 Aug 2021 Shift 1 Paper

Let the principal and rate of interest be $\mathit{₹}\mathit{P}$ and $\mathit{R}\%$ p.a. respectively.
According to the question, from Amount

$9920=\mathit{P}+\frac{\mathit{P}\times \mathit{R}\times 2}{100}$ . . . (i)
. . . (ii)
Eq. (ii) divide by Eq. (i),
$\frac{12800}{9920}=\frac{\mathit{P}\left(1+\frac{5\mathit{R}}{100}\right)}{\mathit{P}\left(1+\frac{2\mathit{R}}{100}\right)}$
$\Rightarrow \frac{40}{31}=\frac{100+5\mathit{R}}{100+2\mathit{R}}$
$\Rightarrow 4000+80\mathit{R}=3100+155\mathit{R}$
$\Rightarrow 75\mathit{R}=900$
$\Rightarrow \mathit{R}=\frac{900}{75}=12\%$