Question

On a 120km track a train travels the first 30km at uniform speed of 30km/hr. how fast must the next 90km so as to average 60km/he for entire trip

Answer 1

Hey mate,
Here is your answer

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

☺ Hope this will help you.