Two pipes A and B would fill a cistern in 24 minutes and 36 minutes respectively. If bothpipes are opened, find when the second pipe must be turned off so that the cistern may be just filled in 16 minutes.

• 12 minutes.
  
  First pipe is opeed for 16 mins and fills 16/24=2/3 cistern
  1/3 cistern is filled by second pipe in 36*1/3=12 min
  so second pipe should be turned off after 12 mins.
• 11 years agoHelpfull: Yes(9) No(2)
• Let t be the time till when both are opened, so
  (1/24 + 1/36)*t + (1/24)*(16-t) = 1
  Solving above equation, we get
  t = 12mins
• 11 years agoHelpfull: Yes(0) No(0)