# Pipes and Cistern- Aptitude Questions and Answers

 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 The second pipe will fill it in (x+10) hours 1/x + (1/(x+10))= 1/12 => (2x+10)/((x)*(x+10))= 1/12 => x2-14x-120=0 => (x-20)(x+6)=0 => x=20 (value can not be -ve ) So, the second pipe will take 30 hours to fill the reservoir Post/View Answer Post comment Cancel Thanks for your comment.! Write a comment(Click here) ...
 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 So 1 hour work of A,B and C =1/6 C closed after 2 hour's, Part filled in 2 hours working together(A,B and C) = 2/6 = 1/3 Remaining part = (1-1/3) = 2/3 A and B can fill remaining in 8 hours, (A + B)'s 8 hour's work = 2/3 So, (A+B)'s 1 hour work = 2/24=1/12 Therefore C's 1 hour's work = [(A+B+C)'s 1 hour]-[(A+B)'s 1 hr work] =(1/6 - 1/12) = 1/12 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 in next, 2 minutes both pipe can fill another 5/12 part. So in 4 minutes A and B are operating alternatively will fill 5/12 + 5/12 = 5/6 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) => 4 minutes + 2/3 minutes = 4(2/3) minutes Or, 4 minutes 40 seconds 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) Part filled B in 1 hr= (1/36) Part filled by (A+B) together in 1 hr=(1/45)+(1/36)=1/20 So, The tank will be full in 20 hr. 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 Hence, required part of the tank to be filled in 1h = 1/6 part 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) => (1/8 - 1/16) = 1/16 Time taken to empty the full tank = 16 min. Hence, time taken to empty the half tank = 8 min 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) => (1/2 - 1/3) = 1/6 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 66 pipes=> ? Amount of work done is same for filling a pipe, So 44*27 = 66*X X = 44*27 / 66 X = 18 66 pipes can fill one tanks in 18 hours. Hence, they will fill 4 tanks in 18*4 = 72 hours 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 : Work done by first tap in 1 min is 1/10 Work done by second tap in 1 min is 1/30 In 5 minutes work done by both pipes is = 5*(1/10 + 1/30) =5*(4/30) =2/3 After 5 min first tap is closed, Now, remaining work is = 1 - 2/3 = 1/3 So, remaining work done by second tap is = 30*(1/3) = 10 After closing first tap, the second tap will be filled the tank completely in 10 minutes. 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 Part filled by B in 1 hour= 1/45 Part filled by (A+B)'s in 1 hour=1/36 +1/45 = 9/180 = 1/20 Hence, both the pipes together will fill the tank in 20 hours 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 =8/60 =2/15 The tank be filled in 15/2 hours= 7 hrs 30 min 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 Therefore the cistern will be filled in 36/5 hours or 7.2 hours 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 =(1/12+1/15) - 1/20 = 1/10 Waste pipe will empty the cistern in 10 minutes. 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 Part filled by the four taps in 1 hour=4/6=2/3 Remaining part=1 -1/2=1/2 2/3 of the tank is filled by four taps in 1 hour let the time taken to fill Remaining part is x Therefore, 2/3:1/2 :: 1:x or x=(1/2)*1*(3/2)=3/4 hours ie 45 min So, the total time taken = 3 hrs + 45 min = 3 hrs 45 min A water tank is two-fifth 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 Part emptied by (A+B) in 1 min= 1/6 - 1/10=1/15 Therefore, 1/15:2/5::1:x or x=((2/5)*1*15)=6 min 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 Then capacity of Q=x/3 liter Capacity of the drum=60x liter Required number of turns= 60x/(x+(x/3))= 60x*3/4x=45 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 Time taken by these two pipes to fill the tank=112/15 hrs Due to leakage, time taken = 7 hrs 28 min + 32 min= 8 hours Therefore, work done by (two pipes + leak) in 1 hr= 1/8 work done by leak n 1 hour=15/112 -1/8=1/112 Leak will empty full cistern n 112 hours