Aptitude - Alligation or Mixture - Discussion
Discussion Forum : Alligation or Mixture - General Questions (Q.No. 3)
3.
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?
Answer: Option
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.
Discussion:
100 comments Page 3 of 10.
Meeran said:
1 decade ago
Ratio was 7:5 initially and 7:9 after drawn 9 lit from A to B.
Hence, Watching only the ratio of A liquid before and after the change we get.
Before : (7/12) * (x-9) Since, said 9 lit drawn and added to B.
After : 7 Given in the question itself as 7:9 ratio.
Since given both are the ratio, equating the both above we get,
(7/12) * (x-9) = 7 => x-9 = 12 => x = 21 lit.
Hence, Watching only the ratio of A liquid before and after the change we get.
Before : (7/12) * (x-9) Since, said 9 lit drawn and added to B.
After : 7 Given in the question itself as 7:9 ratio.
Since given both are the ratio, equating the both above we get,
(7/12) * (x-9) = 7 => x-9 = 12 => x = 21 lit.
Trilok said:
1 decade ago
We need to find how many liters of liquid A present in the can initially. So it is given that ratio is 7:5. So clearly it is a multiple of 7. And, by looking at the options we get the answer as 21.
Vaishali said:
1 decade ago
7:5.
7:9.
7+5 = 12.
9-5 = 4.
9/12*4 = 3.
3*7 = 21.
7:9.
7+5 = 12.
9-5 = 4.
9/12*4 = 3.
3*7 = 21.
Rushita said:
1 decade ago
How is it possible? please give me some explanation.
NITISH said:
1 decade ago
Using allegation method.
At first ratio of 5/12, only B was filled by replacing 9l of mixture. So 9l of B was filled extra to fulfill the can.
1-9/16
--------- = 3:1.
9/16-5/12
Let capacity be x,
1/4*x = 9.
x = 36.
So, B = 15 and A = 21.
At first ratio of 5/12, only B was filled by replacing 9l of mixture. So 9l of B was filled extra to fulfill the can.
1-9/16
--------- = 3:1.
9/16-5/12
Let capacity be x,
1/4*x = 9.
x = 36.
So, B = 15 and A = 21.
Akash said:
1 decade ago
So easy. The answer should be a multiple of 7 as the initial ratio of A:B is 7:5.
And only 21 is in the option which is a multiple of 7. So option C.
And only 21 is in the option which is a multiple of 7. So option C.
Sneha said:
1 decade ago
Why I take 12?
Karthika said:
1 decade ago
We need to subtract 9 liters from mixture only. But why subtract from 2 liquids?
Karthika said:
1 decade ago
Why 7(x-9) and 5(x-9)? Please help me.
Ankita said:
1 decade ago
In the very first explanation how does 20x+21 come into picture? I mean just the 21.
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