A milkman mixed some water with milk to gain 25% by selling the mixture at the cost price. The ratio of water and milk is respectively -

Cost price of 1 litres of milk = Rs. 100
∴ Mixture sold for Rs. 125
= $$\frac{125}{100}$$ = $$\frac{5}{4}$$ litres
∴ Quantity of mixture = $$\frac{5}{4}$$ litres
∴ Quantity of milk = 1 litre
∴ Quantity of water = $$\frac{5}{4}$$ - 1 = $$\frac{1}{4}$$ litre
∴ Required ratio = $$\frac{1}{4}$$ : 1 = 1 : 4