Numerical answer
A vessel contains 72 litres of a milk-water mixture in the ratio 5:1. How many litres of water must be added so that the ratio of milk to water becomes 3:1?
Show answer and solution
Answer: 8
Milk = 72 × 5/6 = 60 L, Water = 72 × 1/6 = 12 L. Adding x litres of water keeps milk fixed at 60 L. We need 60/(12+x) = 3 ⇒ 12+x = 20 ⇒ x = 8. Adding water never changes the milk quantity, only the denominator — this is the key idea in such alligation problems.
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