In a mixture of 60 litres, the ratio of milk and water is 2:1. What amount of water must be added to make the ratio of milk and water as 1:2?

Step 1: Analyze the Initial Mixture

• Total quantity of mixture = 60 litres
• Milk : Water = 2 : 1 → Total parts = 3
• Milk = (2/3) × 60 = 40 litres
• Water = (1/3) × 60 = 20 litres

Step 2: Let the amount of water to be added = x litres

• New water = 20 + x litres
• Milk remains the same = 40 litres
• We want new ratio Milk : Water = 1 : 2

Step 3: Set up the equation

40 / (20 + x) = 1 / 2

Step 4: Solve the equation

2 × 40 = 20 + x  
80 = 20 + x  
x = 60

Answer: 60 litres

We need to add 60 litres of water to make the ratio of milk to water 1:2.

This type of problem is a classic example of ratio adjustment using algebra and is frequently seen in quantitative aptitude tests. It also reinforces concepts of proportion and logical reasoning which are important for competitive exams and real-life resource planning.