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 the correct choice from the following.
A) 10 min.  B) 40 min.  C) 30 min.  D) 20 min.  E) 15 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 x 1/15=1   x/30=1   x = 30 min.   Answer is 30 min.
<result>C</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?