Two pipes A and B can fill a tank in 18 hours and 24 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?
Choose the correct choice from the following choices.
A) 20 hours
B) 15 hours
C) 10 hours
D) 10 2/7 hours
E) 8 hours
Part filled by A in 1 hour = 1/18   Part filled by B in 1 hour = 1/24   Part filled by (A+B) in 1 hour = 1/18 + 1/24 = 7/72   Both the pipes together fill the tank in 72/7 = 10 2/7 hours   Answer is 10 2/7 hours
<result>D</result>
Two pipes A and B can fill a tank in 18 hours and 24 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?