Question

If a person travels 2/5th of a distance​ at 20 km/h, 1/5th of the distance at 30 km/h and rest of the journey at 40 km/h, then what is his average speed for the entire journey?

Answer 1

Let the total distance of the journey be d.

The person travels 2d/5 distance with speed 20km/hr, ie, he takes (2d/5) /20 hours (= 8d hours) to travel that distance.

Similarly he travels​ d/5 distance in 6d hours.

Now, rest of the journey is of 2d/5 km which he travels at a speed of 40km/hr.
He travels that distance in time = (2d/5)/40
= 16d km

{Using time = distance/ speed}

Now, the average speed = total distance/ total time

avg speed = d/(8d+6d+16d)
= d/(30d)
= 1/30 km/hr


That's it! I hope you understand the concept. You just need to calculate the time​ taken for traveling in all separate parts of the journey and calculate the total time.
All the best! Practice more, you will understand it definitely.
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