Aptitude - Pipes and Cistern - Discussion
Discussion Forum : Pipes and Cistern - General Questions (Q.No. 4)
4.
Two pipes A and B can fill a cistern in 37
minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
Answer: Option
Explanation:
Let B be turned off after x minutes. Then,
Part filled by (A + B) in x min. + Part filled by A in (30 -x) min. = 1.
 x |
 |
2 | + | 1 |  |
+ (30 - x). | 2 | = 1 |
| 75 | 45 | 75 |
 |
11x | + | (60 -2x) | = 1 |
| 225 | 75 |
11x + 180 - 6x = 225.
x = 9.
Discussion:
90 comments Page 3 of 9.
Nins said:
1 decade ago
What is the meaning of "1" here?
Shwetha cr said:
1 decade ago
1 indicates complete cistern.
Sameera said:
1 decade ago
1 indicates complete work, a+b=1 means a and b have done a complete work.
Silvi said:
1 decade ago
This is not logical reasoning. By multiplying them with minutes, you can not estimates their unit to be a part.
Hence, the "=1" here is unaccepted. You must provide with minutes unit too.
Hence, the "=1" here is unaccepted. You must provide with minutes unit too.
Ratih said:
1 decade ago
I still don't get the logic. Why you talk about minutes needed and suddenly talk about part.
You can't write it "=1".
You can't write it "=1".
Silvi said:
1 decade ago
If we reverse the answer to the common formula:
9x11/225+21x2/75.
We will get answer = 1.
But we actually want to get answer = 30 minutes, right?
This explanation is clearly not logical and misleading.
We can't assume minutes unit is same with part unit.
You can't multiply them with minutes and suddenly make the equation "=1" because it's clearly not same unit.
9x11/225+21x2/75.
We will get answer = 1.
But we actually want to get answer = 30 minutes, right?
This explanation is clearly not logical and misleading.
We can't assume minutes unit is same with part unit.
You can't multiply them with minutes and suddenly make the equation "=1" because it's clearly not same unit.
Raj said:
1 decade ago
Please tell me how we get 2/75?
ASIF said:
1 decade ago
Simply.
(1-Given time/A's time)*B's time.
= (1-30/75/2)45.
= (1-60/75)*45.
= (1-0.8)*45.
= 0.2*45 = 9.
(1-Given time/A's time)*B's time.
= (1-30/75/2)45.
= (1-60/75)*45.
= (1-0.8)*45.
= 0.2*45 = 9.
Nehal said:
1 decade ago
Hey,
After first step just open the brackets i.e,
2x/75 + x/45 + 60/45 - 2x/75 = 1.
(2x/75 - 2x/75) + x/45 + 60/45 = 1.
0 + x/45 + 4/5 = 1.
Take 1/5 as common,
x/9 + 4 = 5.
x/9 = 1.
x = 9.
No need of complex calculations.
After first step just open the brackets i.e,
2x/75 + x/45 + 60/45 - 2x/75 = 1.
(2x/75 - 2x/75) + x/45 + 60/45 = 1.
0 + x/45 + 4/5 = 1.
Take 1/5 as common,
x/9 + 4 = 5.
x/9 = 1.
x = 9.
No need of complex calculations.
Prakash kumar said:
1 decade ago
Let us understand the problem first, we can easily analyze that Here Pipe A is run for HALF an hour.
Total part filled by part A alone in half an hour is {2/75}*30 = (4/5).
Now (1- (4/5) ) , that is (1/5) part is still remaining. And it is filled by Pipe B and after that it is made off.
So (1/5) part filled by Pipe B in,
= 45*(1/5) = 9 minute.
Hence after 9 minute pipe B will made off.
Total part filled by part A alone in half an hour is {2/75}*30 = (4/5).
Now (1- (4/5) ) , that is (1/5) part is still remaining. And it is filled by Pipe B and after that it is made off.
So (1/5) part filled by Pipe B in,
= 45*(1/5) = 9 minute.
Hence after 9 minute pipe B will made off.
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