A person travels along a straight road due east for the first half distance with speed V1 and the second half with speed V2 . what is the average speed of the person ?????????

       plzzzzzzzzzzzz  if possible answers it before today night ,because its to urgent ;;;;;;;;;;;;;;;;thank u

Lets calculate the time taken by the person to travel the whole distance

so,

for first half of the journey (as time = distance/speed)

t1 = (x/2) / v1

and 

for the second half

t2 = (x/2) / v2

so, total time taken

t = t1 + t2 = (x/2) /v1 + (x/2) / v2

or t = (x/2) [(1/v1) + (1/v2)]

so,

t = x(v1+v2) / 2.(v1v2)

now, the average speed = total distance/ time taken

thus,

average speed, v = x / t

or

v =  x / x(v1+v2) / 2.(v1v2)

finally, the average speed is

v = 2.(v1v2) / (v1 + v2)