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A cistern has two taps which fill it in 12 min and 15 min respectively. There is also a waste pipe in the cistern. When all the three are opened, the empty cistern is full in 20 min. How long will the waste pipe take to empty the full cistern? 
A) 8 minutes
B) 10 minutes
C) 12 minutes
D) 16 minutes
Correct Answer : 10 minutes Explanation : Work done by a waste pipe in 1 min Waste pipe will empty the cistern in 10 minutes. 
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Three pipes A, B and C together can fill a cistern in 6 hours. After working together for 2 hours, C is closed and A and B fill the remaining cistern in 8 hours. Then the time in which the cistern can be filled by pipe C alone will be: 
A) 11 hours
B) 9 hours
C) 12 hours
D) 10 hours
Correct Answer : 12 hours Explanation : Three Pipes A,B and C together filled a tank in 6 hours A and B can fill remaining in 8 hours, (A + B)'s 8 hour's work = 2/3 Therefore C's 1 hour's work C alone can fill the tank in 12 hours 
Two pipes A and B can fill a cistern in 4 and 6 minutes respectively. If both the pipes kept turned on alternatively for one minute each starting from A, how long will it take to fill the cistern? 
A) 3(3/7) minutes
B) 6 minutes
C) 4(2/3) minutes
D) 6(6/7) minutes
Correct Answer : 4(2/3) minutes Explanation : As the pipes are operating alternatively for one minute, thus (A+B)'s 2 minutes job is =(1/4 +1/6) =5/12 Remaining part of cistern= 1  5/6 =1/6 Pipe A can fill 1/4 part of the cistern in 1 minute,and can fill 1/6 part of the cistern in = 4*(1/6) =2/3 minutes Total time taken to fill the Cistern = time taken to fill (5/6 part + 1/6 part) 
Pipe A can fill a tank in 45 hrs and pipe B can fill it in 36 hrs. If both the pipes are opened in the empty tank. In how many hours will it be full? 
A) 10 hr
B) 15 hr
C) 20 hr
D) 28 hr
Correct Answer : 20 hr Explanation : If a pipe can fill a tank in x hours, then : part filled in 1 hour = 1/x Part filled A in 1 hr= (1/45) 
If a pipe fills a tank in 6 h, then what part of the tank will the pipe fill in 1 h? 
A) 1/3
B) 1/6
C) 1/4
D) 1/5
Correct Answer : 1/6 Explanation : Let the pipe can fill a tank in x hours, then part filled in 1 hour = 1/x A pipe fills a tank in 6 h, then the part of tank filled in 1 h = 1/6 
A tap can fill a tank in 16 minutes and another can empty it in 8 minutes. If the tank is already half full and both the taps are opened together, the tank will be ? 
A) Filled in 12 min
B) Emptied in 12 min
C) Filled in 8 min
D) Emptied in 8 min
Correct Answer : Emptied in 8 min. Explanation : Let a pipe can fill a tank in x hours and another pipe can empty the full tank in y hours (where x > y), when opening both the pipes, the net part emptied in 1 hour = (1/y)(1/x) 
One tap can fill a cistern in 2 hours and another can empty the cistern in 3 hours. How long will they take to fill the cistern if both the taps are opened ? 
A) 5 hours
B) 6 hours
C) 7 hours
D) 8 hours
Correct Answer : 6 hours Explanation : Let a pipe can fill a tank in x hours, and another pipe can empty the full tank in y hours (where y> x), then on opening both the pipes, the net part filled in 1 hour = (1/x)(1/y) Hence, time taken to fill the cistern = 6 hours 

44 pipes can fill a large water tank in 27 hours. How many hours it take for 66 pipes to fill four such tanks ? 
A) 72
B) 54
C) 63
D) 84
Correct Answer : 72 Explanation : 44 pipes => 27 hours Amount of work done is same for filling a pipe, So 44*27 = 66*X 
A tank can be filled by one tap in 10 minutes and by another in 30 minutes. Both the taps are kept open for 5 minutes and then the first one is shut off. In how many minutes more is the tank completely filled? 
A) 5
B) 7.5
C) 10
D) 12 Correct Answer : 10 Explanation :
In 5 minutes work done by both pipes is = 5*(1/10 + 1/30) After 5 min first tap is closed, So, remaining work done by second tap is = 30*(1/3) = 10 
Two pipes A and B can fill a tank in 36 hours and 45 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank? 
A) 40 hours
B) 30 hours
C) 20 hours
D) 10 hours
Correct Answer : 20 hours Explanation : Part filled by A in 1 hour=1/36 

Two pipes can fill a tank in 10 hours and 12 hours respectively, while a third pipe empties the full tank in 20 hours. If all the three pipes operate simultaneously, in how much time will the tank be filled? 
A) 7 hrs 15 min
B) 7 hrs 30 min
C) 7 hrs 45 min
D) 8 hrs
Correct Answer : 7 hrs 30 min Explanation : Three pipes 1 hour work =1/10 +1/12 1/20 
A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled? 
A) 7.1 hours
B) 7.2 hours
C) 7.3 hours
D) 7 hours
Correct Answer : 7.2 hours Explanation : Net part filled in 1 hour= 1/4 1/9= 5/36 
If two pipes function simultaneously, the reservoir will be filled in 12 days.One pipe fills the reservoir 10 hours faster than the other. How many hours does it take the second pipe to fill the reservoir? 
A) 25 hours
B) 28 hours
C) 30 hours
D) 35 hours
Correct Answer : 30 hours Explanation : Let the reservoir be filled by the 1st pipe in x hours 
A tap can fill a tank in 6 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely? 
A) 3 hrs 45 min
B) 4 hrs
C) 4 hrs 15 min
D) 5 hrs
Correct Answer : 3 hrs 45 min Explanation : Time taken by one tap to fill the half of the tank =3 hours 2/3 of the tank is filled by four taps in 1 hour Therefore, 2/3:1/2 :: 1:x So, the total time taken = 3 hrs + 45 min = 3 hrs 45 min 
A water tank is twofifth full. Pipe A can fill a tank in 10 min. And B can empty it in 6 min. If both pipes are open, how long will it take to empty or fill the tank completely ? 
A) 6 min. to empty
B) 6 min. to full
C) 9 min. to empty
D) 9 min. to full
Correct Answer : 6 min. to empty Explanation : Clearly, pipe B is faster than A and So, the tank will be emptied. Part to be emptied=2/5 So, the tank be emptied in 6 min 
Bucket P has thrice the capacity as Bucket Q. It takes 60 turns for Bucket P to fill the empty drum. How many turns it will take for both the buckets P and Q, having each turn together to fill the empty drum? 
A) 30
B) 40
C) 45
D) 90
Correct Answer : 45 Explanation : Let the capacity of P be x liters 
Two pipes can fill a cistern in 14 hours and 16 hours respectively. The pipes are opened simultaneously and it is found that due to leakage in the bottom it took 32 min more to fill the cistern. When the cistern is full, in what time will the leak empty it? 
A) 112 hrs
B) 115 hrs
C) 116 hrs
D) 118 hrs
Correct Answer : 112 hrs Explanation : Work done by the two pipes in 1 hour= 1/14+1/16=15/112 