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) 12
(b) 15
(c) 9
(d) 10
The correct answers to the above question in:
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
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Read more basic pipes and cisterns problems Based Quantitative Aptitude Questions and Answers
Question : 1
Three taps A,B and C together can fill an empty cistern in 10 minutes. The tap A alone can fill it in 30 minutes and the tap B alone in 40 minutes. How long will the tap C alone take to fill it ?
a) 40 minutes
b) 16 minutes
c) 24 minutes
d) 32 minutes
Answer »Answer: (c)
Using Rule 1 and 7,
Part of the cistern filled by taps
A, B and C in 1 minute = $1/10$
Part of the cistern filled by taps
A and B in 1 minute
= $1/30 + 1/40 = {4 + 3}/120 = 7/120$
Part of the cistern filled by tap C in 1 minute
= $1/10 - 7/120 = {12 - 7}/120 = 5/120 = 1/24$
Tap C will fill the cistern in 24 minutes.
Question : 2
A tap can fill a cistern in 8 hours and another tap can empty it in 16 hours. If both the taps are open, the time (in hours) taken to fill the tank will be :
a) 24
b) 8
c) 10
d) 16
Answer »Answer: (d)
Part of the cistern filled in 1 hour = $1/8$
Part of the cistern emptied in 1 hour = $1/16$
When both the taps are opened simultaneously, part of cistern filled in 1 hour
= $1/8 - 1/16 = {2 - 1}/16 = 1/16$
Hence, the cistern will be filled in 16 hours.
Using Rule 7,
Here, x = 8, y = 16
Required time = ${xy}/{y- x}$
= ${8 × 16}/{16 - 8}$ = 16 hours
Question : 3
Two pipes A and B can fill a tank in 36 minutes and 45 minutes respectively. Another pipe C can empty the tank in 30 minutes. First A and B are opened. After 7 minutes, C is also opened. The tank is filled up in
a) 45 minutes
b) 39 minutes
c) 46 minutes
d) 40 minutes
Answer »Answer: (c)
Part of the tank filled by pipes A and B in 1 minute
= $1/36 + 1/45 = {5 + 4}/180$
= $9/180 = 1/20$
Part of the tank filled by these pipes in 7 minutes
= $7/20$
Remaining unfilled part
= $1 - 7/20 = {20 - 7}/20 = 13/20$
When all three pipes are opened.
= $1/20 - 1/30 = {3 - 2}/60 = 1/60$
Time taken in filling $13/20$ part
= $13/20$ × 60 = 39 minutes
Required time = 39 + 7 = 46 minutes
Question : 4
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 : 5
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 : 6
Two pipes can fill a tank in 15 hours and 20 hours respectively, while the third can empty it in 30 hours. If all the pipes are opened simultaneously, the empty tank will be filled in
a) 15$1/2$ hours
b) 10 hours
c) 12 hours
d) 15 hours
Answer »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.
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
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