A solution of milk and water contains 60% milk. How many litres of pure milk must be added to 40 litres of this solution to make the milk content 75%?
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Correct answer: D
Explanation
Total solution = 40 liters
Milk content = 60%
Initial amount of milk = 40 × 60/100 = 24 liters
Let's assume x liters of pure milk were added.
New amount of milk = 24 + x
Total volume = 40 + x
New percentage = 75%
(24 + x) / (40 + x) = 75/100
4(24 + x) = 3(40 + x)
96 + 4x = 120 + 3x
x = 24 liters