A fill pipe can fill a tank in 20 hours, a drain pipe can drain a tank in 30 hours. If a system of n pipes (fill pipes and drain pipes put together) can fill the tank in exactly 5 hours, which of the following are possible values of n ?
1)32 2)54 3)29 4)40

• ans =24 . your given option are wrong. let a and b are two pipe used for fill and drain respectively. then workdone by a in one hour=1/20
  and b=1/30
  then amount of water fill in tank=(1/20)-(1/30)=(1/60) that is equal to workdone by two pipe then by one pipe=1/120
  in 5 hour work done is=5120 now for complete work n =24 pipe needee workdone=5*24/120=1.
• 12 years agoHelpfull: Yes(3) No(4)