Q:

Two pipes A and B can fill a cistern in 24 minutes and 30 minutes respectively. Both are opened together, but at the end of 6 minutes the first is turned off. How much longer pipe B will take to fill the cistern?

• 1
  $$ {22{1\over 2}}{minute}$$
• 2
  21 minute
• 3
  24 minute
• 4
  25 minute
• 5
  $$ {23{1\over 2}}{minute}$$