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.
(a)10\%
(b)12\%
(c)15\%
(d)18\%
Answer
Answer (as printed): B
Explanation
Quantity of alcohol in 5 litres solution = 20\% of 5 litres = 1 litres. Quantity of alcohol removed = 20\% of 2 litres = 400 ml. Quantity of alcohol in new solution $=(1000-400) \mathrm{ml}$ $$\text { = } 600 \text { ml. }$$ ∴ Strength of alcohol in new solution $$=\left(\frac{600}{5000} \times 100\right) \%=12 \% .$$
Explanation as extracted from the printed page; notation may be imperfect.