Two taps A and B can fill a cistern in 12 min. and 18 min. respectively . They are turned on at the same time. If the tap A is turned off after 4 min., how long will tap B take to fill the rest of the cistern?
[A] 15 min
[C] 8 min
[B] 12 min
[D] 7 min

• Answer:
  
  For 4 minutes = 4(1/12 + 1/18)
  = 5/9
  
  Remaining part = 1 - 5/9
  = 4/9
  
  Tap B fill the bucket in = 4/9 * 18
  = 8 mins
  
  Explanation:
  
  Basic Formula:
  
  Total work (to fill or empty) = I part + II part = 1
  Find Ist part and subtract it from ‘1’ , then multiply the required section value to find the answer.
• 12 years agoHelpfull: Yes(63) No(3)
• A + B = 1/12 + 1/18 = 5/36
  Aftr 4 min= 5/9
  remaining = 4/9
  B = 4/9 * 18 = 8min
• 11 years agoHelpfull: Yes(13) No(2)
• part filled in 4 minutes=4*(1/12+1/18)=5/9.
  Remaining part=(1-5/9)=4/9.
  So.part filled by B in 1 minutes=1/18
  So,1/18:4/9=1:x or x=(4/9*1*18)=8 min.
  So tank will be full in=(4+8) min=12 mins
  Option (12 min) is ans
• 13 years agoHelpfull: Yes(11) No(23)
• simply find how much time will it take to fill 1/3rd of tank by A and B both.....
  
  so in 4min 1/3 rd will fill by A...
  
  so in 6min 1/3 rd will fill by B
  
  so 12 min more will it take..........
• 13 years agoHelpfull: Yes(3) No(13)
• A and B will fill a cistern for 4 min together=4(1/12 + 1/18)= 5/9.
  Remaining cistern to fill=(1-5/9) = 4/9.
  so, B will take time to fill 4/9 part =(18*4/9)=8 min
  
• 11 years agoHelpfull: Yes(3) No(0)
• gurupreet ji in last the total time to fill the tank (8+4)=12,not only correct answer is 8
  
• 10 years agoHelpfull: Yes(3) No(0)
• jobs done by both 5/9 , rest job =4/9 done in 8 minutes by B.
• 10 years agoHelpfull: Yes(1) No(0)
• In one min A can fill 100/12=8.33% and B=100/18=5.55% ,so in 4 min
  Both can fill 4*(8.33+5.55)=55.5%, then A will stop so the requred ans=(100-55.5)/5.55 which requre 8min.
• 10 years agoHelpfull: Yes(1) No(0)
• Answer:
  
  For 3 minutes = 3(1/12 + 1/18)
  = 5/12
  
  Remaining part = 1 - 5/12
  = 7/12
  
  Tap B fill the bucket in = 7/12 * 18
  = 21/2
  = 10.5 mins
  Explanation:
  
  Basic Formula:
  
  Total work (to fill or empty) = I part + II part = 1
  Find Ist part and subtract it from ‘1’ , then multiply the required section value to find the answer.
  
• 12 years agoHelpfull: Yes(0) No(18)
• [B]12
  done it
• 10 years agoHelpfull: Yes(0) No(3)
• a=12min's
  b=18 min's
  LCM=36
  a alone=3*4=12
  remaining 36-12=24
  B take to fill the cistern=24/2=12 min's
• 10 years agoHelpfull: Yes(0) No(3)
• simple total work we can find by taking lcm of. Both 12 and 18
  Its 36
  Now for 1 hr A fill 3 and B fill 2
  Now they fill for 4 hr both
  So 4*2+3= 20
  Now left is 36-20= 16
  After that b have to complete 16 work
  One day it fill 2
  16÷2= 8 so now work done in 8+4= 12 day
• 8 years agoHelpfull: Yes(0) No(0)