Question : Three pipes, A, B, and C can fill an empty cistern in 2, 3, and 6 hours respectively. They are opened together. After what time should B be closed, so that the cistern gets filled in exactly 1 hr 15 min?
Option 1: 20 min
Option 2: 45 min
Option 3: 30 min
Option 4: 15 min
Correct Answer: 30 min
Solution : Given: Pipes A, B, and C can fill empty cisterns in 2, 3, and 6 hours respectively. Now, Total time taken 1 hr 15 min = $\frac{5}{4}$hrs = 1.25 hrs Let total work = LCM (2, 3, 6) = 6 Work done by A in 1 hr = $\frac{6}{2} = 3$ units Work done by B in 1 hr = $\frac{6}{2} = 2$ units Work done by C in 1 hr = $\frac{6}{6} = 1$ unit Work done by A, B, and C in 1 hr = 3 + 2 + 1 = 6 units A, B, and C are opened together but after $x$ hours pipe B is closed. So, according to the question $x$ × work done by A, B, and C in 1 hour + $(1.25-x)$ × work done by A and C in 1 hour = 6 $⇒ 6x + (1.25-x) × 4 = 6$ $⇒ 2x + 5 = 6$ $⇒ x = 0.5$ hours $= 30$ min Hence, the correct answer is 30 min.
Result | Eligibility | Application | Selection Process | Cutoff | Admit Card | Preparation Tips
Question : Pipes A, B and C together can fill a cistern in 12 hours. All three pipes are opened together for 4 hours and then C is closed. A and B together take 10 hours to fill the remaining part of the cistern. C alone will fill two-thirds of the cistern in:
Question : Pipes A and B can fill a tank in 16 hours and 24 hours, respectively, whereas pipe C can empty the full tank in 40 hours. All three pipes are opened together, but pipe A is closed after 10 hours. After how many hours will the remaining part of the tank be filled?
Question : Pipes A, B and C can fill a tank in 10, 15 and 30 hours, respectively. D is an emptying pipe which alone can empty the full tank in $x$ hours. A, B and C are opened together for 3 hours and then closed. Now D is opened which alone empties the tank in 30 hours. What is the
Question : Pipes A and B can fill a tank in 16 hours and 24 hours, respectively, whereas pipe C can empty the full tank in 40 hours. All three pipes are opened together, but pipe C is closed after 10 hours. After how many hours will the remaining part of the tank be filled?
Question : Three pipes A, B, and C can fill a cistern in 6 hours. After working at it together for 2 hours, C is closed and, A and B fill it in 7 hours more. The time taken by C alone to fill the cistern is:
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile