How can we find the average speed of a journey when one-fourth of the journey is travelled by a particular velocity and remaining journey by another velocity?

let total distance=x

let velocity for x/4 distance=V1

let velocity for another 3x/4 distance=V2

time taken in covering x/4 distance=x/4V₁

time taken in covering 3x/4 distance=3x/4V₂

 average speed=total distance/total time taken

=x/(x/4V₁+3x/4V₂)