A person moves from place A for place B at 12:00 PM at a speed of 12.5 km/h, stayed at place B for 2.5 hours and returned to place A at a speed of 17.5 km/h.  He came back to place A at 8:30 PM. What is the distance between places A and B (in km)?

43.75 km

Total time in journey    8:30 PM - 12:00 PM = 8.5 hours

Total effective time in journey = 8.5 hours - 2.5 hours (rest time) = 6 hours

               A to B   :   B to A

Speed ⇒  12.5     :    17.5

                  5       :       7

Time   ⇒     7       :       5    = 12   (Total)

Total Time = 12R = 6 hrs.

1R = 0.5 hr

So, A's time = 7R = 7 × 0.5 = 3.5

Distance = Speed × Time

              = 12.5 km/h × 3.5 = 43.75 km