Question

To fill a certain tank, pipes A, B and C take 20 minutes, 15 minutes and 12 minutes respectively. If the three pipes are opened every alternate minute, how long will it take to fill the tank?

• A. 5 minutes
• B. 10 minutes
• C. 12 minutes
• D. 15 minutes

Answer 1

Answer: (D)

15 minutes

Answer 2

Part filled by 3 pipes in 3 minutes $=\frac{1}{20}+\frac{1}{15}+\frac{1}{12}=\frac{3+4+5}{60}=\frac{1}{5}$

1/5th of the tank is filled in 3 minutes then whole tank is filled in 5 x 3 = 15min

Hence, option D is the correct answer.The correct option is (D): 15 minutes