P and Q fill a tank working together in 7.5 minutes. If half of the tank is filled by P and the remaining half is filled by pipe Q the tank will get filled in 20 minutes. In how many minutes Q alone can fill the tank and it is known that pipe P tales less time to fill than pipe Q?

• 30 minutes
  
  1 min. filling by P & Q = 1/P + 1/Q = 2/15 ---(i)
  Total time, when half of the tank is filled by P and half by Q = (1/2)/(1/P) + (1/2)/(1/Q) = 20 or
  P+Q=40 ---(ii)
  From (i), (P+Q)/PQ =2/15
  Substituting value of P+Q from (ii), we get 40/PQ=2/15 or PQ=300
  Now P+Q=40 & PQ=300, satisfies for P=10, Q=30 (*P taking less time than Q)
• 7 years agoHelpfull: Yes(8) No(0)
• @devendra, how did u get p=10 and q=30
• 7 years agoHelpfull: Yes(1) No(0)