Two quantities are in a proportional relationship if they can be expressed in general form y = kx, where k is a constant proportionality.
Two quantities x and y are said to vary in inverse proportion, if there exists a relation of the type xy = k between them, k being a constant.
Milk and water are mixed in the proportion 5:2 in container A, and in container B in the proportion, 8:5. In what proportion should quantities be taken from the two vessels as to form a mixture with milk and water in the proportion 9:4?