Question: 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
20
21
25
[A].
[B].
[C].
[D].
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 |
|
= | 7 | ||||||
|
9 |
| 28x – 21 | = | 7 | |
| 20x + 21 | 9 |
252x – 189 = 140x + 147
112x = 336
x = 3.
So, the can contained 21 litres of A.