Question

On a 100km track ,a train travels the first 30 km at a uniform speed of 30 km /hr .How fast must the the train travel for the next 70 km as to average speed 40 km/hr for the entire trip

Answer 1

At average speed of 40km/h for the entire journey:

Time = Distance ÷ Speed = 100 ÷ 40 = 2.5 hours

Time taken for the first part of the journey:

Time = Distance ÷ Speed = 30 ÷ 30 = 1 hour

Time left for the rest of the 70km:

2.5 hour - hour = 1.5 hour

Speed needed for the 70km:

Speed = Distance ÷ Time = 70 ÷ 1.5 = 45.67 km/h

Answer: The train must travel at 45.67 km/h for the 70 km.