Question

A car covers 30 km at a uniform speed of 30 km/hr. What should be its speed for the next 90 km if the average speed for the entire journey is 60 km/hr ?( ans is 90 km/hr speedbut when we try answer comes 9 km/hr)

Answer 1

D1= 30 km ,S1=30km /hr
T1=D1/S1
T1=30/30
T1=1hr

D2=90km , time=T2
Total distance=D1+D2
D=30+90= 120km
Total time=T1+T2
T= 1+T2
Average speed= total distance/ total time
60= 120/1+T2
1+T2=2 , T2= 2-1=1hr
time = 1sec
speed = distance /time
speed=90/1
speed= 90km/hr