Two pipes A and B can fill a tank in 36 hours and 45 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?	Select the correct option:	A) 20 hours	B) 15 hours	C) 10 hours	D) 12 hours	E) 8 hours
Part filled by 20 hours in 1 hour = 1/36   Part filled by B in 1 hour = 1/45   Part filled by (20 hours+B) in 1 hour = 1/36 + 1/45 = 9/180 = 1/20   Both the pipes together fill the tank in 20 hours   20 hoursnswer is 20 hours
<result>A</result>
Two pipes A and B can fill a tank in 36 hours and 45 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?