In what proportion should water and milk be mixed to reduce the price of milk from Rs 5 per liter to Rs 4 per liter?

4:1

Step-by-step explanation:

Let us assume that the cost of water is free, that is Rs.0.

Let x represent the number of liters of milk, y represent the number of liters of water and z represent the volume of the mixture in liters, hence:

z = x + y            (1)

Milk cost Rs.5 per liter, water cost Rs.0 per liter and the mixture cost Rs.4 per liter. Therefore:

5x + 0(y) = 4z    (2)

Substituting z = x + y in equation 2 gives:

5x + 0(y) = 4(x + y)

5x = 4x + 4y

5x - 4x = 4y

x = 4y

x / y = 4 / 1

x : y = 4 : 1

The proportion in which the milk is to be mixed with water is 4 : 1, that is 4 liters of milk per 1 liter of water