Two pipes can fill a tank in 4 hr and 5 hr respectively. If they are turned on alternatively for 1 hr each, the tank will be filled in

• 1st tank = 1/4 tank per hour, 2nd tank = 1/5 tank/ hour
  after 2 hours = 1/4 + 1/5 = 9/20, After 4 hrs = 9/10.
  in 5th hour 1st pipe's turn. remaining = 1/10
  1st tank will take 240/10 = 24 mins to fill the remaining.
  So total 4 hrs 24 mins.
• 12 years agoHelpfull: Yes(24) No(3)
• In first 4 hrs , (2*1/4 +2*1/5) = 9/10 tank will be filled.
  balance 1/10 will be filled in next half hr by second tap ( which fills tank in 5 hrs).
  
  so total 4.5 hrs
• 12 years agoHelpfull: Yes(8) No(12)
• 1st tank = 1/4 tank per hour, 2nd tank = 1/5 tank/ hour
  after 2 hours = 1/4 + 1/5 = 9/20, After 4 hrs = 9/10.
  in 5th hour 1st pipe's turn. remaining = 1/10*4= 0.4hr=24min
  total=4hr 24 min
• 12 years agoHelpfull: Yes(5) No(1)
• Ans= 4 hr 24min
• 12 years agoHelpfull: Yes(3) No(6)