Two pipes A and B can fill a cistern in 37.5 minutes and 45 minutes respectively. This cistern will be filled in half an hour if both the pipes are opened together initially and pipe B is then turned off after X minutes. What is X?	Choose the correct choice
A) 10 minutes
B) 15 minutes
C) 12 minutes
D) 9 minutes
E) 8 minutes
Explanation:   Let B be turned off after X minutes.   Part of water will be filled by A + B in x minutes + After tap B is closed rest filled by A in (30-x) minutes = 1   =&gt; x/(time taken to fill the container by each separately) + 30 - x/(time taken to fill the container by A alone) = 1   =&gt; x(2/75 + 1/45) + (30-x)2/75 = 1   =&gt; 11x + 180 – 6x = 225   Therefore, x = 9 minutes   ANSWER: 9 minutes
<result>D</result>
Two pipes A and B can fill a cistern in 37.5 minutes and 45 minutes respectively. This cistern will be filled in half an hour if both the pipes are opened together initially and pipe B is then turned off after X minutes. What is X?