Question

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

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