A tank is full of water. A drain pipe which can empty the full tank in 60 minutes is opened. 18 minutes later another pipe which can fill the empty tank in 30 minutes is opened. After how much time, in total is the tank full again(in minutes)?

• total 18+18 = 36 min
  suppose tank capacity is 60 ltrs.
  A drain pipe which can empty the full tank in 60 minutes ( @ 1 ltr/min)is opened. 18 minutes later another pipe which can fill the empty tank in 30 minutes( @ 2 ltr /min) is opened. in 18 minutes , 18 ltr water is drained.
  when two pipes are opened, additional 1 ltr/minute ( 2-1=1) is filled in tank.
  To make up for loss of 18 ltrs, it will take 18 minutes.
  
  total 18+18=36 mins
• 12 years agoHelpfull: Yes(9) No(3)
• let tank has capacity= x
  tank emptyin in 60 min.
  speed of ist pipe= x/60 per min
  speed of 2nd(filling pipe)= x/30 per min.
  in 18 min ist has empty the tank= (x/60)*18= 3x/10
  left quantity= x- 3x/10= 7x/10
  2nd is fillin faster 2nd ist is emptying, so we hav to find in which time resulant is 3x/10 so that again tank is filled.
  so (x/30)-(x/60), will result (3x/10) in 18 min.
  
  so time taken is 18 min.
• 12 years agoHelpfull: Yes(3) No(3)
• suppose tank capacity is 60 ltrs.
  A drain pipe which can empty the full tank in 60 minutes ( @ 1 ltr/min)is opened. 18 minutes later another pipe which can fill the empty tank in 30 minutes( @ 2 ltr /min) is opened. in 18 minutes , 18 ltr water is drained.
  when two pipes are opened, additional 1 ltr/minute ( 2-1=1) is filled in tank.
  To make up for loss of 18 ltrs, it will take 18 minutes.
  
• 12 years agoHelpfull: Yes(3) No(1)