A large tank can filled by 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?  Select: A) 10min B) 15min C) 30min D) 25min E) 42min
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   x = 30 min   Answer is 30min
<result>C</result>
A large tank can filled by 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?