Average Speed is defined as the total distance covered by an object divided by the total time taken. It is represented by the formula: Average Speed = Total Distance / Total Time.

From the question, the man went uphill with a speed of 20 km.p.h. and came downhill with a speed of 30 km.p.h. Therefore, the total distance covered and the total time taken need to be calculated in order to determine the average speed for his journey.

Total Distance = Distance Travelled Uphill + Distance Travelled Downhill

Total Time = Time Taken Uphill + Time Taken Downhill

Since the speed for both uphill and downhill is given, the distance travelled and time taken in both directions can be calculated using the formula: Distance = Speed × Time.

Distance Travelled Uphill = 20 km/h × Time Taken Uphill

Distance Travelled Downhill = 30 km/h × Time Taken Downhill

Now, the total distance and total time can be calculated:

Total Distance = Distance Travelled Uphill + Distance Travelled Downhill

Total Time = Time Taken Uphill + Time Taken Downhill

Finally, the average speed can be calculated using the formula: Average Speed = Total Distance / Total Time

Average Speed = Total Distance / Total Time

Therefore, the average speed for his journey is 24 km/h.

Hence, the correct answer is Option D. 24 Km.per hr.

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