A mixture of 30 litres contain milk and water in the ratio

A mixture of 30 litres contain milk and water in the ratio of 7 : 3. How much water should be added to it so that the ratio of milk and water becomes 3 : 7 ?

Quantity of milk in 30 litre mixture

=	30	× 7 = 21 litres
	10

Quantity of water

=	30	× 3 = 9 litres
	10

Suppose x litres more water is added.
According to question,

21	=	3
9 + x	=	7

⇒ 9 + x = 49
⇒ x = 40 litres