Two pipe A and B c an fill a cistern in 32 minutes and 48 minutes respectively. Both the pipes are opened together for some time and then pipe B is turned off. What is the pipe B must be turned off so that the cistern gets filled in 24 minutes ?
Answer & explanation
Correct answer: option 1
The correct answer is option (1) : 12 min
Part of the tank filled by both the pipes in 1 min $=\frac{1}{32}+\frac{1}{48}=\frac{5}{96}$
Let pipe B be turned off after t min
$⇒t×\frac{5}{96}+(24-t)×\frac{1}{32}=1$
$5t+72-3t=96$
$2t=24$
$t = 12$
Hence, pipe B is turned off after 12 min.