[38.3] If a person divides a distance into 3 equal parts and travels the three parts with speeds of 50, 40

For Competitive Exams

If a person divides a distance into 3 equal parts and travels the three parts with speeds of 50, 40 and 30 km/hr respectively, what is his average speed (in km/hr) for the whole journey?

37.5

38.3

Explanation:

Let the total distance be 3x kms.

∴ The distance travelled in each part is x kms.br>

∴ The time taken to cover the three parts is x/50 ,x/40 and x/30 respectively.br>
Now, average speed is total distance covered divided by the total time taken, so we get,br>
Average speed = Total distance/Total timebr>
Average speed = $\dfrac{3x}{(x/50 + x/40 +x/30)}$br>
=$\dfrac{3}{(1/50 + 1/40 +1/30)}$br>
$\dfrac{3}{(12+15+20)/600}$br>
=$\dfrac{1800}{47}$br>
=38.3 kmph

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