80 litre mixture of milk and water contains 10% milk. How much milk (in litres) must be added to make water percentage in the mixture as 80%?

Step 1: Understand the initial setup

• Total mixture = 80 litres
• Milk = 10% of 80 = 8 litres
• Water = 80 - 8 = 72 litres

Step 2: Let x litres of milk be added

• New quantity of milk = 8 + x
• Water remains the same = 72 litres
• New total mixture = 80 + x litres

Step 3: Set up the equation

We want water to be 80% of the total mixture:

Water / (Milk + Water) = 80 / 100
=> 72 / (80 + x) = 4 / 5

Step 4: Solve the equation

72 × 5 = 4 × (80 + x)
360 = 320 + 4x
360 - 320 = 4x
40 = 4x
x = 10

Answer: 10 litres

You need to add 10 litres of milk to make water 80% of the new mixture.