A cistern, when full, is emptied by a waste pipe in 30min., but if a tap (filling souce) is opened, it takes 40 min. to empty the cistern. How long the cistern will take to become full when both the pipes are working?
[A] 180 min
[C] 140 min
[B] 110 min
[D] 160 min

• 
  qstn is wrong
  empty rate of A =1/30 per minute
  empty rate A+fill=1/40
  this says ;;;fill rate =1/30-1/40=1/120
  now fill rate is much much lesser than empty rate so cistern will never be filled ....so qstn is wrong it shud be any other to be predicted rather than full rate ...
• 12 years agoHelpfull: Yes(28) No(7)