Question

On a 120 km track train travelsfirst 20 km in 30km/Hr.What speed should it travel the rest distance to have avg. speed 60km/hr

Answer 1

Speed of the train in the first 30 km, v1 = 30 km/h
Speed of the train in the next 90 km, v2 (to be determined)
Average speed = 60 km/h = (v1 + v2)/2 
                                          = (30 km/h + v2)/2 

⇒ v2 = 90 km/h