RRB NTPC 18 January 2017 Paper

(3) Let two S.I. be x and (2400 – x)
When, S.I. = x, then
P = 5000, T = 4 years, R% = R
and when SI = (2400 – x), then
P = 4000, T = 5 years, R% = R
$\frac{\left(5000\times 4\mathit{R}\times \mathit{x}\right)}{100}$ -------- (i)
or
$\mathit{x}=2400-\mathrm{}\frac{4000\times 5\times \mathit{R}}{100}$--------(ii)
From equations (i) and (ii):
$\mathrm{}\frac{5000\times 4\times \mathrm{}\mathit{R}}{100}=2400-\mathrm{}\frac{4000\times 5\times \mathrm{}\mathit{R}}{100}$
$\Rightarrow 200\mathit{R}=2400-200\mathit{R}$
⇒400R=2400
⇒R=6% p.a.