Three pipes, A, B, & C are attached to a tank. A & B can fill it in 20 & 30 minutes respectively while C can empty it in 15 minutes. If A, B & C are kept open successively for 1 minute each, how soon will the tank be filled?

• in three minute 1/20+1/30-1/15=1/60 part is filled
  3 min--------1/60 parts
  x min--------- 1 part(full)
  
  x=180 min =3 hours
• 8 years agoHelpfull: Yes(34) No(8)
• Time to fill the tank by pipe A = 20 minutes
  
  so part of tank filled in 1 minute by pipe A = 1/20 per minute
  
  Time to fill the tank by pipe B = 30 minutes
  
  so part of tank filled in 1 minute by pipe B = 1/30 per minute
  
  Time to empty the tank by pipe C = 15 minutes
  
  so part of tank emptied in 1 minute by pipe C = 1/15 per minute
  
  So if all the pipes works successively ,
  
  part of tank filled in 1 minute = 1/20
  
  part of tank filled in 2 minute = 1/20 + 1/30 .
  
  part of tank filled in 3 minute = 1/20 + 1/30 - 1/15
  
  =1/60
  
  so after 165 minutes =(165/3)x(1/60) =55/60
  
  after 166 minutes =55/60+1/20=58/60
  
  after 167 minutes =58/60+1/30=60/60
  
  So the answer is 167 minutes
• 8 years agoHelpfull: Yes(27) No(48)
• First of all take L.C.M. of 20,30 and 15 it will give you total size of tank i.e. 60 then divide 60 to 20 it will give how much unit A can fill the tank in 1 minute i.e. 3 unit per minute same as B can fill 2 unit per minute and c can empty 4 unit per minute and then
  A+B-C= 3+2-4 = 1 unit in three minutes because pipes will keep open successively for 1 minute
  so 60*3 =180 minutes
• 8 years agoHelpfull: Yes(9) No(4)
• ans=60 min
  work done=1/20+1/30-1/15=1/60
  s=60 min
• 8 years agoHelpfull: Yes(8) No(9)
• L.C.M of 20,30,15 is 60.
  So total capacity of tank is 60 l.
  So A fills 3 l in 1 minute.
  B fills 2 litres in 1 minute.
  C sends 4 liters in 1 minute.
  So 2+3-4=1
  So water in tank is 1liter per 3 minutes.
  So to fill 60 liters 180 minutes.
• 8 years agoHelpfull: Yes(7) No(2)
• tank filled in 1 min=(1/20+1/30)-1/15
  =5/60-1/15
  =1/60
  
• 8 years agoHelpfull: Yes(6) No(2)
• let 180unit work
  A,B,C haveing spd 9,6,12 unit per min
  now 9+6-12=3 unit
  then 180/3=60
  take 59 whch is almost 60
  59*(9+6-12)=177unit and time=59+59+59=177
  at 178 th min A would open and fill the tank fully
  ans=178min
  
• 8 years agoHelpfull: Yes(4) No(4)
• 60 minutes
• 8 years agoHelpfull: Yes(3) No(0)
• 180 min
  first A is filling the tank then B then C empty it..so total 3 mins=1/20+1/30-1/15=1/60
  So in 1 min=60 x 3=180 mins
• 8 years agoHelpfull: Yes(2) No(2)
• in 1 minute the tank fill 1/60.
  so the tank takes time to fill fully is 60 minute means 1 hour.
• 8 years agoHelpfull: Yes(2) No(0)
• A , B & C = 60 min
• 8 years agoHelpfull: Yes(1) No(1)
• A can filled in 20 min that means A can filled 5% per min
  B can can filled in 30 min that means B can filled 3.33% per min
  c can empty it in 15 min that means C can empty 6.66% per min
  so all three are open successively for 1 min each
  so tank fill after 3 min=(A's fill+B's fill-C's empty)=(5+3.33-6.66)=1.67% tank fill in 3 min
  1 min tank fill=1.67/3=0.556%
  100 % tank fill in =100/0.556=179.86 min ans.
• 8 years agoHelpfull: Yes(1) No(2)
• if we consider all are opened at same time then they will fill in 60 min........... but if we consider one after other then in 3 min they will do 1/60 work done in 3 min .so whole would we done in 180 min
• 8 years agoHelpfull: Yes(1) No(0)
• Tank filled in 1st minute = 1/20
  Tank filled in 2nd minute = 1/20 +1/30
  Tank filled in 3rd minute = 1/20 + 1/30 - 1/15
  Amount of water in Tank after 3 minutes = 1/60
  Hence total time needed to fill the tank = 3*60 = 180
  
• 8 years agoHelpfull: Yes(1) No(0)
• why ? after 165 minute
• 8 years agoHelpfull: Yes(0) No(1)
• I think nearly equal to 69 minutes.
• 8 years agoHelpfull: Yes(0) No(1)
• why ? after 165 minute
• 8 years agoHelpfull: Yes(0) No(1)
• in 1 min.A fills 1/20 part
  B fills 1/30 part and C empty 1/15 part
  If pipes used successively after 3 min part filled is
  1/20+1/30+1/15=1/60 i.e. one round...
  therefore after 59 round part filled is 59/60....and total min required for that is 59*3=177 min.
  and then in next minute pipe A fills the tank fully
  thus total min required are 178 minutes..........
  
• 8 years agoHelpfull: Yes(0) No(2)
• what is the correct answer?
  Admin plz provide it?
• 8 years agoHelpfull: Yes(0) No(0)
• in first minute A fills 1/20 part of tank
  in second minute A & B fills 1/12part of the tank
  in third minute A,B & C fills 1/60 part of the tank
  so,totally after 3 minutes the fills (1/20 + 1/12 + 1/60) part of the tank =9/60 th part of the tank
  then to fill full tank is 20 minutes ( 60/9 x 3/1 = 20)
  
• 8 years agoHelpfull: Yes(0) No(0)
• work done by a in 1 min = 1/20
  work done by b in 1 min = 1/30
  work done by c in 1 min= 1/15
  so portion filled in 1 min = (1/20 + 1/30)-1/15 = 1/60
  1/60 part filled in 1 min
  so 1 part filled in 60 mins = 1 hr
• 8 years agoHelpfull: Yes(0) No(0)
• In three minute 1/20+1/30-1/15=1/60 part is filled
  3 min--------1/60 parts
  so left part =(1-1/60)
  left part=59/60
  if 1/60 part can be filled in 3 mins
  59/60 part can also be fill in (3*60*59)/60=177
  so total time take by A,B,C pipes=177+3=180
• 8 years agoHelpfull: Yes(0) No(0)
• Total work done in 3min=3+2-4.....means 1unit.....so to do 60unit of work it is required total 180min
• 8 years agoHelpfull: Yes(0) No(0)
• ( 1/20 + 1/30 - 1/15 )= 1/60 for 3 minutes
  so 3*60 = 180 minutes
• 7 years agoHelpfull: Yes(0) No(0)