A person travles along a straight road for the first half time with a velocity V1 and the second half time with a velocity V2, then mean velocity is given by
`(V = V1 + V2)/2`
2/V = 1/V1 + 1/V2
V = V1 / V2
V = V2/V1
it will become 2v1v2/v1+v2