A mixture of buttermilk and water has 25% water and 75% is buttermilk, and total amount of mixture is 72 L. How much water should be added so that new mixture contains 40% of water in it?

The original mixture contains 72 liters, of which 25 percent is water, meaning there is 18 liters of water and 54 liters of buttermilk. Adding water changes the total volume but keeps the buttermilk volume constant at 54 liters. In the new mixture, buttermilk must account for 60 percent of the total since water is 40 percent. Therefore, 60 percent of the new total equals 54 liters, making the new total 90 liters. The amount of water to add is 90 minus 72, which is 18 liters.

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