Model 1 Basic Pipes & Cisterns problems Section-Wise Topic Notes With Detailed Explanation And Example Questions
MOST IMPORTANT quantitative aptitude - 3 EXERCISES
The following question based on pipes & cisterns topic of quantitative aptitude
(a) 15$1/2$ hours
(b) 10 hours
(c) 12 hours
(d) 15 hours
The correct answers to the above question in:
Answer: (c)
Using Rule 2,
Part of tank filled in 1 hour when all three pipes are opened simultaneously
= $1/15 + 1/20 - 1/30$
= ${4 + 3 - 2}/60 = 5/60 = 1/12$
Hence, the tank will be filled in 12 hours.
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Read more basic pipes and cisterns problems Based Quantitative Aptitude Questions and Answers
Question : 1
Two pipes, P and Q, together can fill a cistern in 20 minutes and P alone can in 30 minutes. Then Q alone can fill the cistern in
a) 51 minutes
b) 62 minutes
c) 60 minutes
d) 61 minutes
Answer »Answer: (c)
Using Rule 7,
Part of the cistern filled by pipe Q in 1 minute
= $1/20 - 1/30 = {3 - 2}/60 = 1/60$
Required time = 60 minutes
Question : 2
Three pipes P, Q and R can separately fill a cistern in 4,8 and 12 hours respectively. Another pipe S can empty the completely filled cistern in10 hours. Which of the following arrangements will fill the empty cistern in less time than others ?
a) P, Q and S are open.
b) Q alone is open.
c) P and S are open.
d) P, R and S are open.
Answer »Answer: (a)
Using Rule 2 and 7,
Part of the cistern filled in 1 hour
when pipes P and S are open
= $1/4 - 1/10 = {5 - 2}/20 = 3/20$
Hence, the cistern will be filled in $20/3$ hours ≈ 6.6 hours
Part of the cistern filled in 1 hour
when pipes P, R and S are open
= $1/4 + 1/12 - 1/10$
= ${15 + 5 - 6}/60 = 14/60 = 7/30$
Hence, the cistern will be filled in $30/7$ hours ≈ 4.3 hours
Part of the cistern filled in I hour
when pipes P, Q and S are open
= $1/4 + 1/8 - 1/10$
= ${10 + 5 - 4}/40 = 11/40$
Hence, the cistern will be filled in $40/11$ hours ≈ 3.6 hours
Cistern can be filled faster when P, Q & S are open
Question : 3
12 pumps working 6 hours a day can empty a completely filled reservoir in 15 days. How many such pumps working 9 hours a day will empty the same reservoir in 12 days ?
a) 12
b) 15
c) 9
d) 10
Answer »Answer: (d)
Hours/day | Days | Pumps |
6 | 15 | 12 |
↑ | ↑ | ↓ |
9 | 12 | x |
Let x be number of pumps
9 : 6 : : 12 : x = 12 : 15 : : 12 : x
9 × 12 × x = 6 × 12 × 15
$x = {6 × 12 × 15}/{9 × 12}$ = 10
Question : 4
A cistern can be filled with water by a pipe in 5 hours and it can be emptied by a second pipe in 4 hours. If both the pipes are opened when the cistern is full, the time in which it will be emptied is :
a) 20$1/2$ hours
b) 9 hours
c) 18 hours
d) 20 hours
Answer »Answer: (d)
According to the question
Cistern filled in 1 hour = $1/5$ part
Cistern emptied in 1 hour = $1/4$ part
When the both pipes are opened, simultaneously ;
Cistern emptied in 1 hour
= $1/4 - 1/5 = {5 - 4}/20 = 1/20$ part
The time in which it will be emptied = 20 hours.
Using Rule 7,A tap 'A' can fill a tank in 'x' hours and 'B' can empty the tank in 'y' hours. Then (a) time taken to fill the tankwhen both are opened = $({xy}/{x - y})$ : x > yb) time taken to empty the tankwhen both are opened = $({xy}/{y- x})$ : y > x
Here, x = 5, y = 4
Required time = $({xy}/{x - y})$ hrs
= ${5 × 4}/{5 - 4}$ hrs = 20 hrs.
Question : 5
A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?
a) 120 minutes
b) 121 minutes
c) 110 minutes
d) 115 minutes
Answer »Answer: (d)
Using Rule 7,
Part of the tank filled in first two minutes
= $1/20 - 1/30 = {3 - 2}/60 = 1/60$
Part of tank filled in 114 minutes
= $57/60 = 19/20$
Remaining part of cistern will be filled in 115th minute
Question : 6
Two pipes can fill a cistern separately in 10 hours and 15 hours. They can together fill the cistern in
a) 9 hours
b) 6 hours
c) 7 hours
d) 8 hours
Answer »Answer: (b)
Using Rule 1,
Part of the cistern filled by both pipes in 1 hour
= $1/10 + 1/15 = {3 + 2}/30 = 1/6$
The cistern will be filled in 6 hours.
GET pipes & cisterns PRACTICE TEST EXERCISES
Model 1 Basic Pipes & Cisterns problems
Model 2 Filling tank by parts or fractions
Model 3 Opening both taps and leaks
pipes & cisterns Shortcuts and Techniques with Examples
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