A body covers half of the total time with velocities 40 km/hr and 60 km/hr for 2 equal distances and remaining half time with velocity 80 km/hr.find the average velocity of the body for the whole journey?
Please explain.

Let the total time be 2t hours

For the first half time, the body has 2 velocities, 40 km/h and 60 km/h for equal distances.

Let the that distance be d.

The time it takes to cover d is d/40
The time it takes to cover the next d is d/60

The total time is therefore d/40 + d/60 = t

The last trip lasts for t hours.
The distance of the last trip is 80t.

Total distance is 2d + 80t
Total time is 2t

Average velocity = Total distance / Total time

Can you work this out?