A milkman makes a 20% profit by selling milk mixed with water at Rs 9 per litre. If the cost price of 1 litre of pure milk is Rs 10 and water costs nothing, what is the ratio of milk to water in the mixture?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 3 : 1
Alligation works on cost prices, so the selling price is first turned into the cost price of 1 litre of the mixture. Water costs nothing.
Cost price of the mixture \(\displaystyle =\frac{9}{1.2}=\) Rs 7.50 per litre
Milk (Rs 10) \(\propto 7.50-0=7.50\)
Water (Rs 0) \(\propto 10-7.50=2.50\)
Milk : water \(=7.50:2.50=3:1\)
The ratio of milk to water is 3 : 1.