A cistern is two-third full of water. Pipe A can fill the remaining part in 12 minutes and pipe B in 8 minutes. Once the cistern is emptied, how much time will these two pipes take to fill it together completely.

• ANSWER : 14.4 min OR 14 min 24 sec.
  
  SOLUTION :
  
  Empty part of cistern = 1-2/3 = 1/3
  
  A can fill in 1 min = 1/(3*12) = 1/36
  B can fill in 1 min = 1/(3*8) = 1/24
  Both A & B togher fill in 1 min = 1/36 + 1/24 = 5/72
  So, Whole cistern can fill by both in 72/5 = 14.4 min OR 14 min 24 sec.
• 13 years agoHelpfull: Yes(19) No(0)
• A takes 12 min to fill 1/3 part
  so, to fill complete part A takes 36min
  similarly b takes 24 min
  if they work together 1/36+1/24=5/72
  they required=72/5min=14.40min
• 12 years agoHelpfull: Yes(1) No(1)