Two pipes A and B can fill a cistern in 12 and 16 minutes respectively. Both pipes are opened together but 4 minutes before the cistern is full pipe A stop working. How much time will the cistern take to fill?
Answer & explanation
Correct answer: option 1
Pipe A can fill = 12 minutes
Pipe B can fill = 16 minutes
LCM of 12 and 16 = 48 ( total work )
Efficiency of pipe A = \(\frac{48}{12}\) = 4
Efficiency of pipe B = \(\frac{48}{16}\) = 3
total efficiency ( A + B ) = 7
Let A work for 4 minutes more = 4 × 4 = 16
then total work done by ( A + B ) = 48 + 16 = 64
time taken = \(\frac{64}{7}\) = 9\(\frac{1}{7}\)