Question

Pipe A can fill a tank in 12 hours and pipe B can empty the tank in 18 hours. Both the pipes are opened at 6 A.M. and after some time, pipe B is closed. The tank is full at 8 P.M.
What was the time at which pipe B was closed?

• A. 9 AM
• B. 9.30 AM
• C. 10 AM
• D. 10.45 AM
• E. 11.30 AM

Answer 1

The correct option is A

9 AM

The tank was full in 14 hours $\to$ Pipe A worked for complete 14 hours.
Let pipe B worked for $x$ hours.
$\therefore \frac{14}{12}-\frac{x}{18}=1$
$x=3$ hours
Hence, pipe B was closed at 9 A.M.