Two pipes A and B can fill a tank in 36 bours and 46 bours respectively. If both the pipes are opened simultaneously, bow mucb time will be taken to fill the tank?

       Part filled by A in 1 hour = (1/36);

       Part filled by B in 1 hour = (1/45);

        Part filled by (A + B) In 1 hour =(1/36)+(1/45)=(9/180)=(1/20)

       Hence, both the pipes together will fill the tank in 20 hours.