Question

On a 120km track,a train travels the first 30km wat a uniform speed of 30km/h.How fast must the train travel the next 90km so as to average speed about 60km/h for the entire trip?

Answer 1

For these sort of questions you have to look at the time involved. If the person wants to average 60 km/hr for a 120 km trip then it has to take exactly 2 hours. At 30 km/hr for the first 30 km it took an hour. This means the rest of the trip, which is 90 km, has to be covered in the remaining hour. The answer is 90km/hr.