If a car covers 2/5th of the total distance with v1 speed and 3/5th distance with v2 then average speed is
12√v1v2
v1+v22
2v1v2v1+v2
v1v23v1+2v2
Averagespeed=TotaldistancetravelledTotaltimetaken =x2x/5v1+3x/5v2=5v1v23v1+2v2