A vessel contains a mixture of spirit & water. Spirit is 18\%. 8 litres of the mixture is taken out of the vessel, which is again filled with water. If the present percentage of spirit is 15\%, find the quantity of the mixture in the vessel?

Let initial quantity be x liters. Initial spirit = 0.18x. After removing 8 liters of mixture: spirit removed = 0.18 × 8 = 1.44 liters. Remaining spirit = 0.18x - 1.44. This is now 15% of x (since total returns to x after refilling with water): 0.15x = 0.18x - 1.44. Solving: 0.03x = 1.44, so x = 48 liters. Option C (48) is correct.