In 126 liters mixture ratio of milk and water is 5:7. What liters of the mixture should be taken out and replaced with pure milk so that the final mixture contains milk and water in equal proportions?

In a 126L mixture with milk:water = 5:7, we have 52.5L milk and 73.5L water. To make them equal (63L each), we need to add 10.5L milk and remove 10.5L water. When we remove x liters of mixture and replace with pure milk: milk removed = (5/12)x, water removed = (7/12)x. Final milk = 52.5 - (5/12)x + x, Final water = 73.5 - (7/12)x. Setting equal: 52.5 + (7/12)x = 73.5 - (7/12)x, which gives x = 18L. Verification: Remove 18L (7.5L milk, 10.5L water), add 18L pure milk. New milk = 52.5 - 7.5 + 18 = 63L, New water = 73.5 - 10.5 = 63L. Ratio is 1:1.