A person travelled from A to B at 40 km/h and from B to A at 50 km/h.  The entire journey took 6.3 hours.  Find the distance between A and B.

140 km

Speed    →  40   :   50

                   4    :   5

Time      →   5    :   4      =    9 →  ×0.7  → 6.3 (given)

                   ↓        

                 ×0.7

                   ↓       

                  3.5

               Distance = 40 × 3.5 = 140 km