A container contains 40 liters of a mixture of milk and water. The ratio of milk to water in the mixture is 3:2. If 10 liters of this mixture is taken out and replaced with 10 liters of milk, what is the new ratio of milk to water in the container?

Initially, the total mixture = 40 liters. Milk = (3/5) × 40 = 24 liters. Water = (2/5) × 40 = 16 liters. Now, 10 liters of the mixture is removed, which will consist of both milk and water in the ratio 3:2. Milk in 10 liters = (3/5) × 10 = 6 liters. Water in 10 liters = (2/5) × 10 = 4 liters. After removing 10 liters, the remaining milk = 24 - 6 = 18 liters. The remaining water = 16 - 4 = 12 liters. Now, 10 liters of milk is added back. New milk = 18 + 10 = 28 liters. New water = 12 liters. The new ratio of milk to water = 28:12 = 7:3. Correct option: a