A cistern is two-third full of water. Pipe A can fill the remaining part in 12 minutes and pipe B in 8 minutes. Once the cistern is emptied, how much time will they take to fill it together completely?
(A) 12 minutes (B) 12.5 min (C) 14.4 min (D) 10.2 min (E) 14.66 min

• As pipe A takes 12min. to fill remaining one-third it takes 36min. to fill completely. similarly pipe B takes 24min. to fill completely
  so, total time taken by both together is reciprocal of:
  (1/36)+(1/24)=5/72
  ans:14.4 min.
• 14 years agoHelpfull: Yes(16) No(0)
• cistern is 2/3rd full of water that means remaining capacity of cistern is 1/3.
  pipe A can fill 1/3rd of cistern in 12min so it will fill completely it in 12*3=36min.
  pipe B can fill 1/3rd of cistern in 8min so it will fill completely it in 8*3=24min.
  so they together fill the cistern in 1min =1/24+1/36=60/(24*36)=1/14.4
  that means cistern is filled completely=14.4min.
  hence (c) is the ans.
  
  
• 14 years agoHelpfull: Yes(6) No(0)
• ans is c)14.4mins
  two-third of cistern is full.
  so remaining 1/3 need to be full.
  using pipe A, it will take 12 mins to fill the remaining parts.
  that is using pipe A the cistern will be full in 36mins.
  using pipe B,the remaining will be fill in 8 mins.
  that is using pipe b the cistern will be full in 24mins.
  so both together it will take (1/36)+(1/24)=5/72.
  that is 72/5 mins or 14.4mins
  so ans is c)14.4mins
  
• 14 years agoHelpfull: Yes(5) No(0)
• Remaining part=(1-2/3)=1/3
  A take 12 min to fill 1/3 of tank
  A fill complete tank in 3*12=36 min
  same as B fill whole tank in 8*3=24 min.
  A and B fill whole tank together in=36*24/(36+24)min
  ans:14.4 min
• 14 years agoHelpfull: Yes(4) No(0)
• to fill (1/3)rd A takes 12 minutes, To fill full tank 36 minutes
  to fill (1/3)rd B takes 8 minutes, To fill full tank 24 minutes
  (1/A)+(1/B)=(1/(A&B));
  A&B==>when both A and B are combined together to do the work
  ==>
  (1/36)+(1/24)=(1/(A&B))
  A&B=(36*24)/(36+24)=14.4
  
  
  
• 14 years agoHelpfull: Yes(2) No(0)
• let Volume of tank = V ltrs
  time taken by A to fill V/3 ltrs = 12 mins ; therefore, Rate of flow of A = (V/3)/12 = V/36 ltrs/min.
  similarly, Rate of flow of B = V/24 ltrs/min
  Net rate of A + B = V/14.4 ltrs/min ; Hence time taken to fill whole tank (V) by A and B = 14.4 mins.
• 14 years agoHelpfull: Yes(1) No(0)
• Let total capacity of cistern = x . Given here
  A fill x/3 in 12 mins => A fill x/36 in 1 min.
  B fill x/3 in 8 mins => B fill x/24 in 1 min
  A and B can fill x/36 + x/24 = 5x/72 in 1 min.
  so to fill x, they will take 72/5 = 14.4 min.
  So answer is (C)
  
• 14 years agoHelpfull: Yes(1) No(0)
• pipe A fill whole tank in 36m and B in 24m
  then part of tank in 1m=(1/36)+(1/24)=5/72
  then time required 72/5=14.4m
• 14 years agoHelpfull: Yes(1) No(0)
• (C) 14.4 min
• 14 years agoHelpfull: Yes(0) No(2)
• C.14.4 min
• 14 years agoHelpfull: Yes(0) No(1)