SSC CHSL Model Paper 20

Suppose the vessel initially contains 8 litres of liquid.
Let x litres of this liquid be replaced with water.
Quantity of water in the new mixture $=\left(3-\frac{3\mathit{x}}{8}+\mathit{x}\right)\mathrm{litre}$
Quantity of syrup in the new mixture $=\left(5-\frac{5\mathit{x}}{8}\right)\mathrm{litres}$
So, $3-\frac{3\mathit{x}}{8}+\mathit{x}=5-\frac{5\mathit{x}}{8}$
$\Rightarrow 5\mathit{x}+24=40-5\mathit{x}$
$\Rightarrow 10\mathit{x}=16$
$\mathit{x}=\frac{8}{5}$
So, part of the mixture replaced $=\frac{8}{5}\times \frac{1}{8}=\frac{1}{5}$