Aptitude - Pipes and Cistern - Discussion
Discussion Forum : Pipes and Cistern - General Questions (Q.No. 6)
6.
Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:
Answer: Option
Explanation:
| Work done by the waste pipe in 1 minute = | 1 | - |  |
1 | + | 1 |  |
| 15 | 20 | 24 |
| = | |
1 | - | 11 | |
| 15 | 120 |
| = - | 1 | . [-ve sign means emptying] |
| 40 |
 Volume of |
1 | part = 3 gallons. |
| 40 |
Volume of whole = (3 x 40) gallons = 120 gallons.
Discussion:
48 comments Page 2 of 5.
Shyam said:
7 years ago
How this relation come 1/A+1/B+1/C = 1/15?
Third pipe can empty tank that means 1/A+1/B-1/C = 1/15.
Third pipe can empty tank that means 1/A+1/B-1/C = 1/15.
(1)
Vishal gawali said:
7 years ago
We can directly determine the total capacity of tank by taking LCM of 20 24 15 as 120.
Rakhshanda said:
7 years ago
How 3 gallons =1/40?
Somi said:
7 years ago
Thank you @Swapnil.
Somi said:
7 years ago
Thank you @Swapnil.
Swapnil said:
7 years ago
Let , the time taken by waste pipe to empty the tank is x.
Then part feed in one min.
(1/20+1/24) - 1/X = 1/15
11/120 -1/X = 1/15,
11X-120/120X = 1/15,
165X -1800= 120 X,
By solving we get x = 40 min.
So 40 min is the time which is taken by waste pipe to empty the entire tank
In problem it is given that waste pipe discharge 3 gallons per min.
40*3= 120 gallons is a capacity of tank.
Then part feed in one min.
(1/20+1/24) - 1/X = 1/15
11/120 -1/X = 1/15,
11X-120/120X = 1/15,
165X -1800= 120 X,
By solving we get x = 40 min.
So 40 min is the time which is taken by waste pipe to empty the entire tank
In problem it is given that waste pipe discharge 3 gallons per min.
40*3= 120 gallons is a capacity of tank.
(1)
Puja banerjee said:
8 years ago
Thanks for the explanation @Bhakta B Monger.
Prasna said:
8 years ago
Take the LCM of 24 and 20, you will get the Answer is 120.
Tubai said:
8 years ago
Your logic is most acceptable or easy to me, Thanks @Rabi.
Pritesh Bhawsar said:
8 years ago
I have the best solution here.
take LCM of 20,24 = 120
Pipe c can empty 3 gallon/minute.
120/3 = 40 minute.
-----------------------------|
minute | efficiency |
-------------|---------------|
a = 20 | 6 |
b = 24 | 5 |
c = 40 | 3 |
******************************
(a+b-c) --> 11-3 = (+8)
120/8 = 15 minute.
120-gallon tank will fill in 15 minutes,
A can fill in 24 minutes or 5 gallons/minute,
B can fill in 20 minutes or 6 gallons/minute.
C can empty in 40 minutes or 3 gallons/minute <---question says.
take LCM of 20,24 = 120
Pipe c can empty 3 gallon/minute.
120/3 = 40 minute.
-----------------------------|
minute | efficiency |
-------------|---------------|
a = 20 | 6 |
b = 24 | 5 |
c = 40 | 3 |
******************************
(a+b-c) --> 11-3 = (+8)
120/8 = 15 minute.
120-gallon tank will fill in 15 minutes,
A can fill in 24 minutes or 5 gallons/minute,
B can fill in 20 minutes or 6 gallons/minute.
C can empty in 40 minutes or 3 gallons/minute <---question says.
(1)
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