A vessel contains a 32 litre solution of acid and water in which the ratio of acid and water is 5 : 3. If 12 litres of the solution is taken out and 7.5 litres of water is added to it. Then what is the ratio of acid and water in the resulting solution?

Initially, the 32L solution has 20L acid and 12L water (5:3 ratio). When 12L is removed, the ratio stays the same, so 7.5L acid and 4.5L water are removed, leaving 12.5L acid and 7.5L water. After adding 7.5L water, the final amounts are 12.5L acid and 15L water, which simplifies to 5:6. The key insight is that removal maintains the ratio, while addition only affects the component being added.