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 ? Choose one.
A) 15 min
B) 20 min
C) 27.5 min
D) 30 min
E) None
Solution   Part filled by (A + B) in 1 minute	= (1/60 + 1/40)   = 1/24.   Suppose the tank is filled in x minutes.   = 4/8.   Then,   ‹=›x/2(1/24 + 1/40) = 1   ‹=› x/2×1/15 = 1   x= 30 min.   Answer 30 min
<result>D</result>
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 ?