A dairyman pays ₹ 6.4 per litre of milk. He then adds water in the milk and sells the mixture at ₹8 per litre, thereby making a 37.5% profit. What is the proportion of water to milk, in the milk received by the customers ?
1
1 ∶ 15
2
1 ∶ 10
3
1 ∶ 20
4
1 ∶ 21