Question

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

Answer 1

expected average speed=60kmph

distance=120km.

so total time taken should be 2hours for the entire trip

but 1 hour has been taken to cover 30km

so rest distance =90 km

rest time =1 hour

hence the train should run at a speed greater than 90kmph