Aptitude - Pipes and Cistern
Exercise : Pipes and Cistern - General Questions
- Pipes and Cistern - Formulas
- Pipes and Cistern - General Questions
- Pipes and Cistern - Data Sufficiency 1
- Pipes and Cistern - Data Sufficiency 2
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.
7.
A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?
Answer: Option
Explanation:
Suppose pipe A alone takes x hours to fill the tank.
Then, pipes B and C will take | x | and | x | hours respectively to fill the tank. |
2 | 4 |
1 | + | 2 | + | 4 | = | 1 | |
x | x | x | 5 |
7 | = | 1 | |
x | 5 |
x = 35 hrs.
8.
Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?
Answer: Option
Explanation:
Let the cistern be filled by pipe A alone in x hours.
Then, pipe B will fill it in (x + 6) hours.
1 | + | 1 | = | 1 | |
x | (x + 6) | 4 |
x + 6 + x | = | 1 | |
x(x + 6) | 4 |
x^{2} - 2x - 24 = 0
(x -6)(x + 4) = 0
x = 6. [neglecting the negative value of x]
9.
Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?
Answer: Option
Explanation:
Part filled by A in 1 min = | 1 | . |
20 |
Part filled by B in 1 min = | 1 | . |
30 |
Part filled by (A + B) in 1 min = | 1 | + | 1 | = | 1 | . | ||
20 | 30 | 12 |
Both pipes can fill the tank in 12 minutes.
10.
Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?
Answer: Option
Explanation:
Part filled in 4 minutes = 4 | 1 | + | 1 | = | 7 | . | ||
15 | 20 | 15 |
Remaining part = | 1 - | 7 | = | 8 | . | ||
15 | 15 |
Part filled by B in 1 minute = | 1 |
20 |
1 | : | 8 | :: 1 : x | |
20 | 15 |
x = | 8 | x 1 x 20 | = 10 | 2 | min = 10 min. 40 sec. | ||
15 | 3 |
The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec.
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