Pipes A and B can fill an empty tank in 10 hours and 15 hours respectively. If both are opened together in the empty tank, how much time will they take to fill it completely?
Number of hours Pipe A requires to fill an empty tank : 10 hours
Number of hours Pipe B requires to fill an empty tank : 15 hours
Amount of water filled by Pipe A in empty tank in one hour: 
Amount of water filled by Pipe B in one hour: 
Amount of water filled by Pipe A and Pipe B together in one hour: 
= 
= 
They can fill the tank together in 6 hours.
14