Question

on a 200 km track A train travels first 50 km at a uniform speed of 40 km per hour how fast the train must travel the next 150 km so as to maintain the average speed of 60 km per hour for the whole journey. tell it to me steps by step.

Answer 1

The speed of train for 50 km = 40 km/h
We know that speed = distance/time
40 km/h = 50/time
time = 50/40 = 5/4 h

Let the speed for next 150 km be x km/h
distance = 150 km
time = distance /speed = 150/x h

Total distance = 150 km + 50 km = 200 km
Total time = 5/4 + 150/x = (5x + 600)/4x h

Average speed = total distance/total speed

60 km/h = 200/[(5x + 600)/4x]
60 = 800x/(5x + 600)
300x + 36000 = 800x
800x - 300x = 36000
500x = 36000
x = 36000/500
x = 72 km/h 

The train has to travel with 72 km/h for next 150 km to maintain an average speed of 60 km/h


Hope this helps you.