A car moving on a straight road  covers 25th of the total distance with  speed'v1'  and  covers35th  remaining distance with speed "v2" then average speed of car  is

Let the total distance is ‘S’ A car covers 25th of the total distance with v1 speed in time t1  35th of the total distance with v2 speed in time t2speed=distancetime time=distancespeed t1=25Sv1=2S5v1;     t2=3S5v2    Average speed =Vav=total  distancetotal  time substitute,Vav=St1+t2 Vav=S2S5v1+3S5v2 Vav=SS52v1+3v2  Vav=52v2+3v1v1v2  Average speed  =5v1v23v1+2v2