Question

a personcoversonethirdoftotaldistanceat x m/s. and one fourthoftotaldistanceat 9m/s. findthe average speedofperson.

Answer 1

Let us assume that the person travels 1m
A/c to the question
he covers 1/3m at xm/s
so time taken to cover 1/3m
=dist./speed={1/3}/x=1/3xsec

Similarly, he covers 1/4m at 9m/s
so time taken to travel 1/4m
=1/4/9=1/36sec

Average speed
=total distance traveled/time taken to travel that distance
={1/3+1/4} / {1/3x+1/36}

On simplifying you will get
avg. speed = 21x/(12+ x)

Hope it helps... :)