A can contains a mixture of two liquids A and B is the ratio 7 : 5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7 : 9. How many litres of liquid A was contained by the can initially?

A can contains a mixture of two liquids A and B is the ratio 7 : 5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7 : 9. How many litres of liquid A was contained by the can initially?

A. 10 B. 20 C. 21 D. 25 Answer: Option C Explanation: Suppose the can initially contains 7x and 5x of mixtures A and B respectively. Quantity of A in mixture left = 7x - 7 x 9 litres = 7x - 21  litres. 12 4 Quantity of B in mixture left = 5x - 5 x 9 litres = 5x - 15  litres. 12 4 7x - 21 4 = 7 5x - 15  + 9 4 9 28x - 21 = 7 20x + 21 9  252x - 189 = 140x + 147  112x = 336  x = 3. So, the can contained 21 litres of A.