A large tanker can be filled by two pipes A and B in 60 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 the correct choice from the following answers
A) 17 min  B) 18 min  C) 15 min  D) 30 min  E) 20 min
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 * 1/15 = 1 =&gt; x = 30 min.   Answer:30 min
<result>D</result>
A large tanker can be filled by two pipes A and B in 60 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?