Question 60

To reach point B from point A, at 4pm, Sara will have to travel at an average speed of 18 kmph. She will reach point B at 3 pm if she travels at an average speed of 24 kmph. At what average speed should Sara travel to reach point B at 2 pm ?

Solution

average speed = (total distance ) /(total time)

Let her time taken to finish race with 18km/hr average speed be y hours

And distance covered in both cases is same

So

D = 18 × y.....(1)

D = 24 x (y-1)....(2)

From equation 1 and 2

y = 4 hours

And D = 72 km

Now if she need to reach at 2pm i.e in 2 hours then the average speed = 72/2 = 36 km/hr

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