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

• the term successively and NOT SIMULTANEOUSLY.AT THE END OF 3 mts, i/60 part of the tank is filled.we have to consider a three-minute block starting from 3 mts, 6 mts,9 mts....etc upto 177 mts. at the end of 165 mts,55/60 part of the tank was filled. at the end of the next suceessive minutes,i.e, 166,167th minute, the part filled is 5/60.so 55/60+5/60. this means the whole tank is filled at the end of 167 th minute.
• 11 years agoHelpfull: Yes(39) No(0)
• 3 taps together fill in 1/60 in 1 min..as they opened one after other it takes 3 min to fill 1/60 of the tank..
  1/60 filled in 3 min
  60/60 can be filled in 3*60=180 min
• 11 years agoHelpfull: Yes(26) No(21)
• 
  In one minute pipe A will fill = 1/20
  In two minute pipe A and B will fill = 1/20 +1/30
  In three minute pipe A, B and C will fill = 1/20 +1/30 - 1/15
  = 1/60
  Let the number intervals of three minutes be x(because each one is open for 1 min each)
  x/60 +1/20 +1/30 = 1
  x + 5 = 60
  x = 55
  then 55*3+2=167
  (after 55 intervals of 3 minutes pipe A pipe B will take 1 minute each i.e 2 minutes)
  
  
• 11 years agoHelpfull: Yes(25) No(3)
• 167.........correct
  
• 10 years agoHelpfull: Yes(11) No(1)
• ans is 60 min=1 hr
  
  A's 1 min work=1/20
  B's 1 min work=1/30
  total work done by A and B in 1 min=1/20+1/30=1/12
  C's 1 min work=1/15
  Therefore A,B,C 1 min work=1/12-1/15=1/60
  (substraction is done bcoz C is emptying the tank)
  Hence total time taken=60 min=1 hr
• 11 years agoHelpfull: Yes(10) No(23)
• please note the term successively and NOT SIMULTANEOUSLY.AT THE END OF 3 mts, i/60 part of the tank is filled.we have to consider a three-minute block starting from 3 mts, 6 mts,9 mts....etc upto 177 mts. at the end of 177 mts, 59/60 part of the tank was filled. at the end of the next minute,i.e, 178th minute, the part filledis 59/60 plus 1/20 which is 62/60. this means the whole tank is filled at the end of 178 th minute.
• 11 years agoHelpfull: Yes(7) No(7)
• Pls note this statement
  If A,B and C are kept open successively for 1 minute each, how soon will the tank be filled?
  
  Here each tap is opened successively for 1 minute.
  3 taps together fill 1/60 tank in 3 minutes when opened one by one for i min each.
  last 1/20 tank will be filled by tap A in last 1 minute.
  First 19/20 or 57/60 tank will be filled in 57*3 = 171 minutes.
  
  so total time taken to fill tank = 171+1= 172 mins.
  
• 11 years agoHelpfull: Yes(4) No(18)
• time taken by pipe A to fill the tank in 1 minute=1/20
  time taken by pipe B to fill the tank in 1 minute=1/30
  time taken by pipe C to empty the tank in 1 minute=1/15
  Total Time=1/20+1/30-1/15=1/60
  so answer will be=60 mintues=1hr
• 11 years agoHelpfull: Yes(2) No(13)
• A,B together can fill the tank in 12min(ab/(a+b))
  C can empty the tank in 15min.
  if each pipe is kept open for 1min then A+B=2min
  A&B together in 12min where as in 2min 1/6th part is filled.
  Now in next min C is opened,for 15min it can empty the tank where as in 1min it can empty only 1/15th part of the tank.
  So in 3min A,B fills and C empties,So 1/6-1/15=1/10
  in 3min 1/10th part of the tank is filled
  So in 30min tank will be filled.
  
  
  The Answer is 30min.
• 11 years agoHelpfull: Yes(1) No(15)