Two pipes A and B can fill a tank in 4 hours and 5 hours respectively. If they are turned up alternatively for one hour each,then time taken to fill the tank is:
1. 2 hrs 15mins
2. 4 hrs 24mins
3. 5 hrs
4. 3 hrs

• A's 1 hr work = 1/4
  B's 1 hr work = 1/5
  A is opened at the 1st hr...
  Part of tank filled in 1st hr = 1/4
  B is opened at the 2nd hr...
  Part of tank filled in 2nd hr = 1/4+1/5 = 9/20
  In 2 hrs ---> 9/20 part filled
  In 4 hrs --> x part filled
  x = 4/2 * 9/20
  x = 18/20
  
  So in 4 hrs part of tank filled = 18/20 => 9/10
  Remaining to be filled = 1 - 9/10 = 1/10
  
  So in 5th hr, A ll be kept opened...
  A ll fill 1/4 part --> In 1 hr
  A ll fill 1/10 part -->In x hr
  x = 4/10 = 2/5hrs => 2/5 * 60 mins => 24mins
  
  So total time taken = 4 hrs + 24 mins
  
  Ans : (2) 4hrs 24mins
• 10 years agoHelpfull: Yes(72) No(2)
• L.C.M of 4hr and 5hr will be 20units..
  now A can fill 5u in 1hr and B can fill 4u in 1hr.
  (5u+4u)+(5u+4u)=18u in 4hr[since 1 combination of 5u and 4u will take 2hr].
  remaining 2u will be filled by pipe A.
  5u will take=60mins
  hence 1u =60/5min=12mins
  hence 2u will take 12*2=24mins.
  so a total of 4hr 24mins will be taken by A and B to fill the tank.
• 10 years agoHelpfull: Yes(10) No(0)
• lets say the volume of tank is 20..in 1 hr A fills 5 parts,next 1hr B fills 4 parts,next 1hr A-5parts,nxt 1hr B-4parts..tot 4hrs..left 2 be filled 2 parts outta 20 now...A can fill 5 parts in 60 mins..he can fill 1 part in 5/60=12mins..2 parts in 12*2=24mins.so tot=4hrs24mins
• 10 years agoHelpfull: Yes(7) No(1)
• 4 hrs 24 mins
  
• 10 years agoHelpfull: Yes(2) No(3)
• option 2.) 4 hrs 24 min
  in 2 hrs A fills the tank 1/2
  in 2 hrs b fill the tank 2/5
  now its turn for A and he will fill the remaining 1/10 tank in 24 min.
• 9 years agoHelpfull: Yes(1) No(0)
• LCM of 4,5=20
  A=5C/hr
  B=4C/hr
  A B A B A
  5 4 5 4
  60 min->5
  x ->2
  x=24min
• 8 years agoHelpfull: Yes(1) No(0)
• 4hour24min
• 7 years agoHelpfull: Yes(1) No(0)
• answer is 4 hrs 24 mins
• 10 years agoHelpfull: Yes(0) No(2)
• 2. 4 hrs 24 min
• 10 years agoHelpfull: Yes(0) No(4)
• 4 hrs 24mins
• 10 years agoHelpfull: Yes(0) No(2)
• 4 hours 24 minutes
• 10 years agoHelpfull: Yes(0) No(1)
• A and B combine work 2 hour work=1/4+1/5=9/20
  4-hour work =9/20+9/20=9/10
  remaining work=1-9/10=1/10
  now it's A's turn so =1/10*4=2/5
  to convert it into minute
  5 - 2
  60 - X
  cross multiplication x=60*2/5= 24 min
  So Ans is 4hr and 24min
• 8 years agoHelpfull: Yes(0) No(0)
• LCM of 4 and 5=20
  1 day work of each A and B,
  A=20/4=5
  B=20/5=4
  AB in 2hrs =9 units
  AB in 4hrs =18 units
  20-18 =2
  
  2 units remaining,
  
  A can do 5 units in 1 hr,
  So, A can do 1 unit in 60/5 =12mins
  Thus, 2 units in 24 mins
  
  hence the answer 4hrs 24mins
• 5 years agoHelpfull: Yes(0) No(0)