Question

On a journey of 100 km on a national highway, a car travels the first 40 km with a uniform speed of 60 km/hr. How fast should the car travel for the next 60 km so that an average speed of 80km/hr is maintained for the whole trip?​

Answer 1

Answer:

Average speed =speed /2

So 120 km per hour

Answer 2

Answer:

Total distance to be covered = 120 Km

Overall average speed for the entire journey = 60 Km/hr

Overall average speed = Total distance / total time taken

60 Km/hr = 120Km / total time

therefore, the total time required = 120 Km / 60 Km/hr = 2 hrs

For the first part of the journey,

30 Km was covered at an average speed of 30 Km/hr,

Time taken = Distance / speed = 30 Km / 30 Km/hr = 1 hr

For the second part of the journey,

Distance left = 120 Km - 30 Km = 90 Km

Time left = Total time - Time taken by first part of the journey

Time left = 2 hrs - 1 hr = 1hr

The average speed required for the second part of the journey to achieve an overall average speed of 60 Km = Distance left / Time left = 90 Km / 1 hr = 90 Km/hr