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.

**Practical matters:**

**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**Respond to****Explanation:**

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**Answer: B****Explanation:**

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**Answer: C****Explanation:**

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**Answer: C****Explanation:**

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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