Correct Answer - Option 3 : 15 litres
Given:
Total amount of mixture = 45 l
Ratio of milk and water = 4 : 1
Calculation:
Amount of milk = (4/5)45 = 36 l
Amount of water = 45 - 36 = 9 l
Let x litres of water to be mixed to make the milk and water ratio 3 : 2
Then, according to the question:
36/(9 + x) = 3/2
⇒ 24 = 9 + x
⇒ x = 15
∴ 15 litres of water must be added.