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2014-09-02T07:34:29+05:30

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Total distance S

Time to cover the first 1/3 of  S =  t1 = (S/3) / v1 = S/(3 v1)
Time to cover the second 1/3 of S = t2 = (S/3)/v2 = S/(3 v2)
Time to cover the last 1/3 of S = t3 = (S/3 ) / v3 = S/ (3v3)

Total time = t =  S/3 [ 1/v1 + 1/v2 + 1/v3 ]

Let v = average speed

v = S / t        So 1/v = t / S

1/ v = 1/3  [ 1/v1 + 1/v2 + 1/v3 ]


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