Question 756507
Pipe A can fill 1/3 of a tank in an hour
Pipe B can fill 1/2 of a tank in an hour.
         1/3 + 1/2 = 1/x
 Using common denominator 6x
         2x + 3x = 6
              5x = 6
               x = 6/5 hours
                 = 72 mins for a full tank
                 = 2/3 *72 = 48 mins to fill 2/3 of a tank.
Hope this helps.
:-)