A mixture contains alcohol and water in the ratio of 4 : 3. If 5 litres of water is added to the mixture the ratio becomes 4 : 5. The quantity of alcohol in the given mixture is = ?

	Alcohol	:	Water
	4	:	3
Let	4x	:	3x

∴ 5 litres of water is added to the mixture
$$\eqalign{ & \Rightarrow \frac{{4x}}{{3x + 5}} = \frac{4}{5} \cr & \Rightarrow 20x = 12x + 20 \cr & \Rightarrow 8x = 20 \cr & \Rightarrow x = \frac{{20}}{8} \cr & \Rightarrow x = \frac{5}{2} \cr & {\text{Quantity of alcohol}} \cr & \Rightarrow {\text{4}} \times \frac{5}{2} = 10\,{\text{litres}} \cr} $$