two pipes A and B fill a cistern in 15 and 20 min respectively,while third pipe C can empty the tank in 30 min.if the three pipes are opened simultaneously for one min each.how long will it take to fill the cistern?

• 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  let job will be 60 unit
  so , speed of pipes are a=4,b=3 and c=-2;
  a+b+c=5;
  total time ==60/5=12 minute
• 8 years agoHelpfull: Yes(1) No(0)
• 1/30-(1/20+15)
  1/30-160=2-1/60=1/60 i.e it will take 60 mins to fill the cistern.
• 8 years agoHelpfull: Yes(0) No(3)
• pipe A fill 1/15 tank in 1 min
  pipe B fill 1/20 tank in 1 min
  pipe C empty 1/30 tank in 1 min
  in 3 mins tank will fill=1/15+1/20-1/30=1/12
  in 1 min=1/36
  then tank will fill in 36 mins.
• 8 years agoHelpfull: Yes(0) No(1)