Question

Two pipes A and B can fill a tank in 6 hours and 8 hours respectivley. If both the pipes are opened together, then after how many hours should B be closed so that the tank is full in 4 hours ?

• A. 3
• B. 8
• C. 8/3
• D. 2/3

Answer 1

Answer:

C. 8/3

Total work = LCM(6, 8) = 24 efficiency of pipe A = 24/6 = 4 efficiency of pipe B = 24/8 = 3 let after x hours should B be closed so that the tank is full in 4 hours 4 × 4 + 3 × x = 24 16 + 3x = 24 3x = 24 - 16 = 8 x = 8/3