a motor car covers 1/3 part of total distance with v1=10km/hr second 1/3 part with v2=20 km/hr and rest 1/3 part v3=60km/hr. what is the average speed of the car?

Happy to help you out, but please show us what you've attempted to solve this problem. Hint: average speed = total distance covered divided by total time taken. So figure the distance covered and the time taken for each segment and add them up.