A mixture of 150 liters of wine and water contains 20% water. How much more water should be added so that water becomes 25% of the new mixture?

Step 1: Understand the initial mixture

• Total quantity of the mixture = 150 liters
• Water is 20% of the mixture ⇒ Water = 20% of 150 = 30 liters
• Wine = 150 - 30 = 120 liters

Step 2: Let the additional water to be added = x liters

• New quantity of water = 30 + x
• Total new quantity of mixture = 150 + x
• We want water to be 25% of the new mixture

Step 3: Form the equation

(30 + x) / (150 + x) = 25 / 100

Step 4: Solve the equation

(30 + x) / (150 + x) = 1 / 4

Cross multiply:
4(30 + x) = 150 + x
120 + 4x = 150 + x
4x - x = 150 - 120
3x = 30
x = 10

Answer: 10 liters

You should add 10 liters of water to make the water content 25% of the new mixture.

This is a classic example of a mixture and alligation problem. By keeping the original amount of wine unchanged and adding water, we adjust the percentage composition of the mixture. These types of problems are common in quantitative aptitude tests, especially in competitive exams, and help strengthen understanding of ratio and percentage manipulations.