Roshni travelled at the speed of 66 km/h while going from point A to point B and returned via the same route at the speed of 92.4 km/h. What was Roshni’s overall average speed during the two-way journey?

Question : Roshni travelled at the speed of 66 km/h while going from point A to point B and returned via the same route at the speed of 92.4 km/h. What was Roshni’s overall average speed during the two-way journey?

77 km/h

79.2 km/h

79 km/h

78 km/h

Solution: $\require{cancel}$

যাতায়াতের গড় গতিবেগ = $ \cfrac{2xy}{x+y}$ [যেখানে x হল যাওয়ার গতিবেগ এবং y হল ফেরার গতিবেগ]
এখানে যাওয়ার গতিবেগ 66 km/h এবং ফেরার গতিবেগ 92.4 km/h.
∴ যাতায়াতের গড় গতিবেগ = $\cfrac{2 \times 66 \times 92.4}{66+92.4} $
$ = \cfrac{2 \times 66 \times 92.4}{158.4} $
$ = \cfrac{\cancel{2} \times \cancel[red]{66} \times \cancelto{77}{924}}{\cancelto{\cancelto[red]{\cancel{12}}{24}}{1584}} $
$= 77$ km/h.

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