a cistern consists of 3 pipes. By the help of 1st and 2nd pie the tank gets filled in 10 hours and 15 hours respectively but by the help of 3rd pipe tank becomes empty in 5 hours. At 8 a.m., 1st pipe was opened. At 9 a.m., 2nd pipe was also opened with 1st. At 10 a.m., 3rd pipe was also opened with 1st and 2nd. When the tank becomes filled or empty?

• cistern filled by first pipe in 1 hr=1/10and second pipe=1/15. cistern emptied by 3rd pipe= 1/5. tank filled from 8a.m-9a.m by first pipe=1/10. tank filled by first and second pipe from 9a.m-10a.m=(1/10+1/15)=1/6. tank filled in this 2hr=1/6+1/10=4/15. tank emptied in 1hr when all three pipes are open=[1/5-(1/10+1/15)]=1/30. time required to empty the tank= 4/15*30= 8 hours. i.e 6p.m
• 10 years agoHelpfull: Yes(30) No(4)
• the total work will be 30litre(lcm of 10,15,5)
  A fill 3 liter in a hour
  B fill 2 litre in a hour
  C empty 6 liter in a hour
  a+b+c will empty 1 litre in a hour
  now a will fill liter 3 till 9 am
  a and b will fill total 8 liter till 10 am
  but working together they empty 1 liter in a hour
  so they will empty 8 liter in 8 hour i.e. 10am+8 hr=6pm
  they will empty tank till 6 pm
  
• 10 years agoHelpfull: Yes(23) No(1)
• Tank is empty at 6 p.m.
  let take x is hours of 1st pipe opened
  if tank is empty(x/10)+((x-1)/15)-((x-2)/5)=0
  then x=10 hrs. so at 6 p.m. tank is emptied.
• 10 years agoHelpfull: Yes(21) No(5)
• let total tank capacity=30 L
  in 1h 1st pipe can fill=3L
  2nd pipe=2L
  &(1st+2nd)pipes =5L
  3rd pipes = -6L
  
  so in 1hour total =+5-6= -1L
  @9a.m tank has=3L water
  @10 = 3L+5L=8L
  @11=8L-1L=7L
  so every hour tank looses 1L of water.
  so @6p.m it will be empty.!!
• 10 years agoHelpfull: Yes(5) No(0)
• let 300lt be the capacity of tank.
  now, for 1st pipe : 300/10=30lt/hr fills
  for 2nd pipe : 300/15=20lt/hr fills
  for 3rd pipe : 300/5=60lt/hr empties
  
  so from 8am-9am, 30lt is filled
  from 9-10 am, 30+20lt is filled
  total = 30+(30+20)lt=80lt
  from 10-11am, (30+20)lt is filled again
  total =130lt
  but now 3rd pipe is started which empties 60lt
  so now total is 130-60=70lt
  
  we can see now total outgoing is 10 more than incoming water flow so from now each hr 10lt will be emptied.
  So 70/10=7hrs more from 11am
  resulting to 6pm.
• 10 years agoHelpfull: Yes(3) No(0)
• 1st pipe can fill the tank in 10 hrs, so it'll fill 10% of the tank in 1 hour.
  1st and 2nd together can fill it in x hours which is found by
  
  1/10 + 1/15 = 1/x
  => x=6 hrs.
  So in 1 hour, they'll together fill 1/6th of the remaining of the tank.
  => 1/6 * 90% of the tank = 15% . So now 25% of the tank is filled.
  Now 1st , 2nd and 3rd can together fill in y hours which is given by
  1/10 + 1/15 - 1/5= 1/y
  => y= 7.5hrs
  Now, 100% of tank is filled in 7.5hrs.
  so 75% of tank will be filled in 5.6 hrs
  So THE TANK WILL BE FILLED AT TIME 10A.M.+5.6HRS = 3:36 P.M approximately.
• 10 years agoHelpfull: Yes(1) No(2)
• answer is it is filled
  in 9 hours i.e 6pm
• 10 years agoHelpfull: Yes(1) No(9)
• ans is tank is getting emptied.
• 10 years agoHelpfull: Yes(1) No(0)
• soltn:- let capacity of cistern is x.
  1st pipe fill the cistern in 1 hour= x/10.
  2nd pipe fill the cistern in 1 hour= x/15.
  3rd pipe can empty the cistern in 1 hour=x/5.
  so from 8 a.m to 10 a.m total cistern filled = x/10+x/15 => x/6
  In next hour 3rd pipe is opened for empty the cistern so that total fill water
  => x/6+x/6(both pipe 1 n 2 are also opend)-x/5= 2x/15.
  so with in 3 hours cistern is filled = 2x/15
  remaining cistern to fill x-2x/15= 13x/15 .
  3 hours +18 hours for 12x/15+ 1.5 hour for x/15= 2x/15+12x/15+x/15=> x
  so cistern will be filled 6:30 am on next day.
  
  
• 10 years agoHelpfull: Yes(0) No(9)
• Speed 30 20 -60(empty)
  Time 10 15 -5
  Dist 300 300 300 (L.C.M of 10,15,5)
  
  At 8 am: 30litres/hr filled
  At 9 am: 30 litres+20 litres/hr filled
  At 10 am: =10 litres emptied from the already filled level ( 30+(30+20)-10=70)
  At 11 am: 3 Pipes empties 10 litres/hr & we know that speed * time = distance
  how much time it need to empty the 70 litres is
  10*T= 70 ----> T=70/10=7 hours
  7 hours from 11 am means it is 6 pm.
  
  
• 10 years agoHelpfull: Yes(0) No(1)
• 8 HOURS IS CORRECT
• 10 years agoHelpfull: Yes(0) No(4)
• in 1 hr 10% of tank is filled
  in 2nd hour 16.67 + 10=26.67% of tank is filled
  for remaining 73.33 part
  the tank eventually gets emptied in 1 hr i.e. at 11.00 am
  
• 10 years agoHelpfull: Yes(0) No(2)
• Tank is empty..
  LCM=(5,10,15)=30.
  so total unit is 30 .
  1st tank filled 3unit in 1hr
  2nd tank filled 2unit in 1hr
  3rd tank empties 6unit in 1hr..
  so when 1st and 2nd get opened it fills upto 5unit ..
  when 3rd tank is open at 10.00 a.m, it empties the tank bcoz 6>5 so no water is there...
  so ans is tank is emptied..
• 10 years agoHelpfull: Yes(0) No(0)
• Tank will not get
  empty . It will be filled...read the question again. Both option r there.
• 8 years agoHelpfull: Yes(0) No(0)