A large tanker can be filled by two pipes A and B in 10 and 5 hours respectively. How many hours will it take to fill the tanker from empty state if A and B fill it together?
Pick
A) 3hr 20min  B) 3hr 50min  C) 4hr  D) 4hr 10min  E) 4hr 15min
Part filled by 3hr 20min in 1hr = 1/10   Part filled by B in 1hr = 1/5   part filled by 3hr 20min+B = 1/10 + 1/5 = 3/10   Both the pipes can fill the tank in = 10/3 hours = 3 hr 20min   3hr 20minnswer is 3hr 20min
<result>A</result>
A large tanker can be filled by two pipes A and B in 10 and 5 hours respectively. How many hours will it take to fill the tanker from empty state if A and B fill it together?