Six pipes are fitted to a water tank. Some of theses are inlet pipes and the others outlet pipes. Each inlet pipe can fill the tank in 9h and each outlet pipe can empty the tank in 6h. On opening all the pipes, an empty tank is filled in 9h. The number of inlet pipes is
(a) 2
(b) 4
(c) 3
(d) 5

• let no of inlet pipe=x
  no of outlet pipe=6-x
  now,work done by inlet pipe in 1 hr=1/9
  work done by outlet pipe in 1 hr=1/6
  so, a/c to problem, (x/9)-[1/6(6-x)]=1/9
  solving this equation, we get x=4
  so no of inlet pipe=4
• 10 years agoHelpfull: Yes(6) No(0)
• Total no. of pipes=6.
  Let no. of inlet pipes be x.
  Then, no. of outlet pipes will be (6-x).
  Part of tank filled by 1 inlet pipe in 1h= 1/9.
  So, Part of tank filled by x inlet pipes in 1h= x/9.
  Similarly,
  Part of tank emptied by 1 outlet pipe in 1h=1/6.
  So, Part of tank emptied by (6-x) outlet pipes in 1h= (6-x)/6.
  Now when both of them are opened at the same time:-
  Part of tank filled in 1h= (x/9) - (6-x)/6 = (15x-54)/54.
  in 9h tank filled= ((15x-54)*9)/54 = (15x-54)/6, which must be equal to 1
  (as tank gets filled in 9h)
  So, ((15x-54)/6 = 1.
  => (15x-54)=6.
  => 15x=60.
  => x=4.
  Thus the solution is:- there are 4 inlet pipes and 2 outlet pipes.
  
  Option (b)
• 10 years agoHelpfull: Yes(6) No(0)
• let there are x inlet pipes.
  work done by inlet =1/9
  work done by outlet=1/6
  here 6-x is the outlets
  x/9-(6-x)/6=1/9
  5x=20
  x=4
  then there will be 4 inlet pipes the will to fill the tank.
• 10 years agoHelpfull: Yes(2) No(0)
• If there are 6 pipes then every time after 9h filled tank will get emptied in 6h. so to get tank fully filled 2 times both will get balance and thenafter that 4th pipe will fill tank . So 4 inlet pipes are required.
• 9 years agoHelpfull: Yes(1) No(0)