A cistern has three pipes,A, B and C. The pipes A and B can fill it in 8 and 12 hours respectively and C can empty it in 6 hours. If the pipes are opened in order at 1, 2 and 3 A.M. When will the cistern be empty? Choose the correct option
A) 9 AM	B) 12 AM	C) 8 AM	D) 11 AM	E) 10 AM
1 to 2 = 1/8   2 to 3 = 1/8 + 1/12 = 5/24   After 3 AM = 1/8 + 1/12 - 1/6 = 1/24   1/8 + 5/24 = 1/3   1 h ---- 1/24   ? ----- 1/3   8 hours ==&gt; 11 AM   Answer:11 AM
<result>D</result>
A cistern has three pipes,A, B and C. The pipes A and B can fill it in 8 and 12 hours respectively and C can empty it in 6 hours. If the pipes are opened in order at 1, 2 and 3 A.M. When will the cistern be empty?