A large tanker can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half ?
A. 15 min
B. 20 min
C. 27.5 min
D. 30 min

• ans is D. 30 min.
  
  let total time consumed in filling the tank is n.
  (A+B)'s 1 minute work is 1/60 + 1/40 and (A+B) will take half of total time ie
  
  (n/2)(1/60 + 1/40)----------(1)
  
  and rest half will be filled by B only in half of total time means (n/2)(1/40)--(2)
  
  (1)+(2)
  
  (n/2)(1/60 + 1/40) + (n/2)(1/40)=1
  
  n=30
• 10 years agoHelpfull: Yes(8) No(2)
• ans is D 30 min
  as in 1 min a can fill 1/69 th part and b can fill1/40 th part
  together they can fill 1/60+1/40 =1/24 th part
  now, let total time taken be x min
  so for half time b fills so part filled by b in x/2 min=x/80th
  and for other half time ,partfilled by a and b together is=1/48th
  so 1/48+1/80=1/30
  =30 min
• 9 years agoHelpfull: Yes(2) No(1)
• 
  Part filled by (A + B) in 1 minute = 1/60 + 1/40 = 1/24 .
  
  
  
  Suppose the tank is filled in x minutes.
  
  
  Then, x/2 ( 1/24 + 1/40) = 1
  
  
  
  
  x/2 x 1/15 = 1
  
  
  
  x = 30 min.
  
• 9 years agoHelpfull: Yes(1) No(1)
• a+b 1 min work = 1/60+1/40=1/24
  
  let if tank is filled in x min
  x/2(1/24+1/40)=1
  so, x=30
• 9 years agoHelpfull: Yes(0) No(0)