One pipe fills in 4 hrs and another in 5hrs when they both work alternately
how much time will be taken to fill the tank.

• The que is little incomplete..as it should be stated that which pipe will start first..due to which we will find minimum time..In 1 hour pipe A will fill 0.25 tank and pipe B will fill 0.2 tank so in 4 hour total work completed is 0.9..for remaining 0.1 work we will take for efficient pipe B..it will take time..
  (0.1/0.25)=0.4 hour =24 minute...so total time is 4 hour 24 minute
• 9 years agoHelpfull: Yes(25) No(3)
• one pipe fills the tank in 4 hrs so part filled by pipe in 1 hr= 1/4
  another pipe fills the tank in 5 hrs so part filled by this pipe in 1 hr= 1/5
  when both the pipes fill the tank in 1 hr = 1/4+1/5 = 9/20
  so the time will be take to fill the tank full = 20/9 hrs or 2.23 hrs
• 8 years agoHelpfull: Yes(10) No(9)
• both work together can fill 9/20 in 1 hour
  9/20*2=18/20 woek in 4 hour
  rest work =1-18/20=2/20=1/10
  1/10 work done by first pipe which take 4*1/10 h=24 min.
  so total time=4 h24 m
• 8 years agoHelpfull: Yes(6) No(0)
• let the work be 100%
  now a can fill in 4 hr it means in 1 hour a can fill 25% of tank
  similarly b can fill 20% of tank in 1 hr
  so they work alternately
  25%+20%+25%+20%+10%
  4 hour 40 minutes
• 9 years agoHelpfull: Yes(3) No(17)
• if both pipes are opened together then the solution will be like this
  (In 1 hr )
  both fill together 1/4 + 1/5 of the tank = 9/20
  similarly in 2 hr = 9/20*2= 18/20
  2/20 of tank is still left
  9/20 of tank can be filled in =60 min
  therefore 2/20 of tank can be filled in 13.13mins
  total time taken 2hr 13 (1/3)mins
• 8 years agoHelpfull: Yes(2) No(1)
• 4 hour 24 minute
• 8 years agoHelpfull: Yes(1) No(1)
• a's 1 hour work=1/4;
  b's 1 hour work=1/5;
  total work=1/4+1/5=9/20.
  20/9hours
• 8 years agoHelpfull: Yes(1) No(1)
• work done by both a and b = 1/4 + 1/5 = 9/20
  so,total time taken to complete the work if both work together=20/9 hrs
  time taken to fill the tank if they work alternatively= 2*20/9=40/9 hours
• 8 years agoHelpfull: Yes(1) No(0)
• answer is 209 hours
• 8 years agoHelpfull: Yes(0) No(8)