From 5 litres of a 20% solution of alcohol in water, 2 litres of solution is taken out and 2 litres of water is added to it. Find the strength of alcohol in the new solution.

Answer: Option B

Quantity of alcohol in 5 litres solution = 20% of 5 litres = 1 litre
Quantity of alcohol removed = 20% of 2 litres = 400 ml
Quantity of alcohol in new solution :
= (1000 - 400)ml
= 600 ml
∴ Strength of alcohol in new solution
$$\begin{array}{rl}& =\left(\frac{600}{5000}\times 100\right)\%\\ & =12\%\end{array}$$