If a person divides a distance into 3 equal parts and travels the three parts with speeds of 50 40 a...........

Quant (SSC) Time & distance

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

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Explanation:

Let the total distance be 3x kms.
∴ The distance travelled in each part is x kms.
∴ The time taken to cover the three parts is x/50, x/40 and x/30 respectively,
Now, average speed is total distance covered divided by the total time taken, so we get,
Average speed = total distance /total time
Average speed = 3x / (x/50 + x/40 + x/30)
= 3 /(1/50 + 1/40 + 1/30)
= 3 / (12 + 15 + 20 /600)
= 1800 /47 = 38.3 km/hr