A train moves with a speed of 30 km/hr in the first 15 minutes, with another speed of 40 km/hr the next 15 minutes and then with a speed of 60 km/hr in the last 30 min. Calculate average speed of train for this journey

average speed =total  distancetotal time  s1 =v1 t1;s2 = v2 t2  ;s3 =v3 t3 average speed =( v1 t1 +v2 t2 +v3 t3)/ t1  +t2 +t3                                30(15/60)+40(15/60)+60(30/60)(15/60+15/60+30/60)                                  =47.5km/hr                                      =47.5×518 =13.2m/s