A container holds 200 litres of a solution of acid and water, having 30% acid by volume. Atul replaces 20% of this solution with water, then replaces 10% of the resulting solution with acid, and finally replaces 15% of the solution thus obtained, with water. The percentage of acid by volume in the final solution obtained after these three replacements, is nearest to

Start: 60 acid, 140 water. 1. Replace 20% (40L) with water: 40L removed (12 acid, 28 water). Remaining: 48 acid, 112 water. Add 40L water: 48 acid, 152 water. 2. Replace 10% (20L) with acid: 20L removed (4.8 acid, 15.2 water). Remaining: 43.2 acid, 136.8 water. Add 20L acid: 63.2 acid, 136.8 water. 3. Replace 15% (30L) with water: 30L removed (9.48 acid, 20.52 water). Remaining: 53.72 acid, 146.28 water. Add 30L water: 53.72 acid, 146.28 water. Final % = 53.72 / 200 = 26.86%. Nearest is 27.