For a train that travels from one station to another at a uniform speed of 40 kmh−1 and returns to same station at speed of 60 kmh−1 then its average speed is

Train travels from one station to another with a speed 40 kmh−1 in time  t1Train returns to the same station with a speed 60 kmh−1 in time  t2 Average speed=total distancetotal time---(1)Let total distance is ‘2S’ speed=distancetime ⇒time=distancespeed substitute, t1=S40;   t2=S60;    t1+t2=t=total time Average speed=2St1+t2 substitute t1  ,t2 values Average speed=2SS40+S60 Average speed=240+6060×40  Average speed=2×60×4040+60 Average speed=48×100100 Average speed=48 kmh−1