A cistern has three pipes, A, B and C. The pipes A and B can fill it in 3 and 4 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?
Choose the correct choice from the following answers.
A) 1 PM  B) 5 PM  C) 4 PM  D) 3 PM  E) 2 PM
1 to 2 = 1/3   2 to 3 = 1/3 + 1/4 = 7/12   After 3 AM = 1/3 + 1/4 - 1/2 = 1/12   1/3 + 7/12 = 11/12   1 h ---- 1/12   ? ----- 11/12   11 hours ==&gt; 2 PM   Answer:2 PM
<result>E</result>
A cistern has three pipes, A, B and C. The pipes A and B can fill it in 3 and 4 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?