Two pipes A and B can fill a cistern in 20 and 30 minutes respectively, and a third pipe C can empty it in 40 minutes. How long will it take to fill the cistern if all the three are opened at the same time?

Related Mcqs:

1. Two pipes A and B can separately fill a cistern in 60 min and 75 min respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened, then the cistern is full in 50 min. In how much time, the third pipe alone can empty the cistern?

   A. 90 min
   B. 100 min
   C. 110 min
   D. 120 min

2. Two pipes A and B can separately fill a cistern in 10 and 15 minutes respectively. A person opens both the pipes together when the cistern should have been was full he finds the waste pipe open. He then closes the waste pipe and in another 4 minutes the cistern was full. In what time can the waste pipe empty the cistern when fill?

   A. 7 min
   B. 8 min
   C. 9 min
   D. 10 min

3. A cistern has two taps which fill it in 12 min. and 15 min.respectively   There is one outlet pipe in the cistern.  When all the taps & pipe are opened, the empty cistern is full in 20 min.  How long will the waste pipe (outlet) take to empty the full cistern ?

   A. 10 min
   B. 20 min
   C. 30 min
   D. 40 min

4. Three pipes A, B and C can fill a tank from empty to full in 30 minutes, 20 minutes and 10 minutes respectively. When the tank is empty, all the three pipes are opened. A, B and C discharge chemical solutions P, Q and R respectively. What is the proportion of solution R in the liquid in the tank after 3 minutes?

   A. 5/11
   B. 6/11
   C. 7/11
   D. 8/11

5. Two pipes can fill a tank in 18 minutes and 15 minutes. An outlet pipe can empty the tank in 45 minutes. If all the pipes are opened when the tank is empty, then how many minutes will it take to fill the tank?

   A. 12
   B. 13
   C. 11
   D. 10

6. A cistern has three pipes, A, B and C. The pipes A and B can fill it in 4 and 5 hours respectively and C can empty it in 2 hours. If the pipes are opened in order at 1, 2 and 3 A.M. When will the cistern be empty?

   A. 3 PM
   B. 7 PM
   C. 4 PM
   D. 5 PM

7. Two taps can separately fill a cistern 10 minutes and 15 minutes respectively and when the waste pipe is open, they can together fill it in 18 minutes. The waste pipe can empty the full cistern in?

   A. 7 min
   B. 13 min
   C. 23 min
   D. 9 min

8. A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 28 minutes. When both pipes are opened, find when the cistern will be full?

   A. 60 min
   B. 80 min
   C. 70 min
   D. 48 min

9. Pipe A can fill a tank in 16 minutes and pipe B cam empty it in 24 minutes. If both the pipes are opened together after how many minutes should pipe B be closed, so that the tank is filled in 30 minutes?

   A. 20
   B. 24
   C. 23
   D. None of these

10. pipes P and Q would fill a cistern 18 and 24 minutes respectively. Both pipes being opened, find when the first pipe must be turned off so that the cistern may be just filled in 12 minutes?

    A. after 12 mins
    B. after 9 mins
    C. after 8 1/2 mins
    D. after 10 mins