A milkman makes 20% profit by selling milk mixed with water

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A milkman makes 20% profit by selling milk mixed with water at 9 per litre. If the cost price of 1 litre pure milk is 10, then the ratio of milk and water in the mixture is

1. 3 : 1
2. 4 : 1
3. 3 : 2
4. 4 : 3

Correct Option: A

Milk : Water = K : 1
∴ S.P. = (K + 1) × 9
C.P. = 10K
Gain = 9 – K

Gain % =	9 − K	× 100
	10K

⇒	9 − K	× 100 = 20
	10K

⇒ 90 – 10K = 20K
⇒ 30K = 90 ⇒ K = 3
∴ Ratio = 3 : 1