LIC AAO 12 May 2013 Paper

Suppose a container contains x units of liquid from which y units are taken out and replaced by water. After n operations the quantity of pure liquid = x ${\left(1-\frac{\mathit{y}}{\mathit{x}}\right)}^{\mathit{n}}$ units
Remaining water = 30 ${\left(1-\frac{3}{30}\right)}^2$
= $\frac{30\times 9\times 9}{100}$ = 24.3 units