Question

A tank has two inlet pipes which can fill the empty tank in 12 hours and 15 hours working alone and one outlet pipe which can empty the full tank in 8 hours working alone. The inlet pipes are kept open for all the time but the outlet pipe was opened after 2 hours for one hour and then again closed for 2 hours then once again opened for one hour. This pattern of outlet pipe continued till the tank got completely filled. In how many hours the tank has been filled, working on the given pattern?

• A. 8 hours 24 minutes
• B. 10 hours 15 minutes
• C. 9 hours 10 minutes
• D. 9 hours 6 minutes

Answer 1

The correct option is C 9 hours 10 minutes

Efficiency of two inlet pipes A and B = 8.33 + 6.66 = 15% Efficiency of two inlet pipes A and B along with an outlet pipe
C = 8.33 + 6.66 - 12.5 = 2.5%

In 9 hours 97.5% tank will be completely filled. On the 10th hour 2.5% (remaining capacity) will be fill by pipe. A, B with its 15% efficiency.
Thus, A will take $=\frac{2.5}{15}=\frac{1}{6}hour=10$ minutes
Therefore, total time = 9 hours and 10 minutes.