The average speed of Dolly is 24kmph.
Let the total distance be 4x km.
Distance covered by car at 60kmph = 4x/2 = 2x
Distance covered by bus at 30kmph = 2x/2 = x
Distance covered by walking at 10kmph = 2x/2 = x
We have to find the average speed of the car for the whole journey.
We know that,
Average speed = Total distance/Total time
Total distance = 4x km
Total time = 2x/60 + x/30 + x/10 = x/30 + x/30 + x/10 = (x +x + 3x)/30 = 5x/30 = x/6 hours
Hence,
Average speed = 4x/(x/6) = (4x)*(6/x) = 24 kmph
To learn more about average speed, here:-
brainly.com/question/12322912
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