Question #128787

a train travels 50 km in half hour. it the stops at a station for 20 mins, before traveling for 2 hours at an average speed of 90 km/h what was the trains average speed over the whole journey

Expert's answer

By definition, the average speed is:

where "l_{tot}" is the total distance covered by the train in time "T_{tot}".

The distance covered during the first part of the journey is 50 km, during the second part is 0 km and during the third part "90km\/h\\cdot 2h = 180" km. Thus:

The time spent on the first part of the journey is 0.5h, on the second part "20\/60 = 1\/3 \\space h" and on the third part 2h, The total time is:

The average speed wil be:

**Answer. **81.2 km/h.

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