one car moving in a straight line covers one third distance in 20km/h and rest in 60km/h. find the average speed

36 km/h

Explanation:

If d is the total distance, then the time spent driving at 20 km/h is:

t₁ = (d/3) / 20

t₁ = d / 60

And the time spent driving at 60 km/h is:

t₂ = (2d/3) / 60

t₂ = d / 90

So the total time is:

t = t₁ + t₂

t = d/60 + d/90

t = d/36

The average speed is the total distance divided by total time:

s = d / t

s = d / (d/36)

s = 36

The average speed is 36 km/h.