Posted: Date Posted – 11:01 PM, Tue – 10 May 22
Hyderabad: This article follows the last article on the preparation for the police sub-inspector recruitment competition. Here are some practical questions and solutions on the subject of Time and work.
Pipes and Cisterns:
Type of pipe:
Entrance : A pipe connected to a reservoir or reservoir for filling is called an inlet.
Exit: A pipe connected to a tank and used to empty it is called an outlet.
Example: A tank can be filled with water through one hose in 5 hours and it can be emptied through a second hose in 4 hours. If both pipes are open, find the time needed to empty the tank?
Answer: 8 p.m.
Either: Time taken by the tanks 5h, 4h, take LCM of 5.4 = 20 (see table)
Follow the red arrow
Now the net speed of both tanks will be -1.
To calculate the time taken, divide 20/-1 = 20.
1. If A can do a job in 5 days, B in 10 days and C in 30 days, they can do it together in
A. 3 days B. 4 days C. 5 days D. 6 days
If A can do work in n days, work done by A in 1 day = 1/n
Work done by A in 1 day = 1/5
Work done by B in 1 day = 1/10
Work done by C in 1 day = 1/30
A+B+C 1 working day = 1/5 + 1/10 + 1/30 = (6+3+1)/30 = 1/3
If P does 1/n work in one day, P can finish the work in n days
Therefore, A+B+C can do a job in 3 days.
Shortcut: LCM of Sum of factors = 30/6 + 3 + 1 = 30/10 = 3 days.
2. A and B can do a job in 6 days and A alone can do it in 9 days. Only B can do it in ____ days
A.16 B.18 C.20 D.22
Work done by A+B in 1 day = 1/6
Work done by A in 1 day = 1/9
Work done by B in 1 day = (1/6) – (1/9)= 1/18
Therefore, B can complete a job in 18 days
3. A and B can do a job in 12 days, B and C in 15 days and C and A in 20 days. They can do it together in ____ days
A.30 B.20 C.10 D.5
Work done by A+B in 1 day = 1/12
Work done by B+C in 1 day = 1/15
Work done by C+A in 1 day = 1/20
By adding we get 2(A+B+C) 1 working day = 1/12 + 1/15 + 1/20 = (5+4+3)/60 = 1/5
(A+B+C) 1 working day= (1/5) * (1/12) = 1/10
Therefore, A+B+C can do a job in 10 days
4. A and B can do a job in 15 and 20 days, that is. With the help of C, if they can do it in 5 days, then only C can do it in ____ days
A.10 B.11 C.12 D.13
Work done by A in 1 day = 1/15
Work done by B in 1 day = 1/20
Work done by A+B in 1 day = (1/15) + (1/20) = (4+3)/60 = 7/60
Work done by A+B+C in 1 day = 1/5
Work done by C in 1 day = (1/5) – (7/60) = 1/12
Therefore, C can complete a job in 12 days.
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