Question

A train travels the first 15 km at a uniform speed of 30 km/h; the next 75 km at a
uniform speed of 50 km/h; and the last 10 km at a uniform speed of 20 km/h.
Calculate the average speed for the entire train journey.

Answer 1

Given

First 15km at a uniform speed of 30 km/h.

Next 75km at a uniform speed of 50 km/h.

Last 10km at a uniform speed of 20 km/h.

Hence

Time 1st=Distance/Speed=15/30

Time 2nd=Distance/Speed=75/50

Time 3rd=Distance/Speed=10/20

Solution

Total time=15/30+75/50+10/20

Total time=150+450+150/300

By solving,

Total time=750/300=5/2

Total distance=15+75+10=100km

Average speed=100/5/2=100×2/5=40

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Hence the answer is 40km/hour

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