Physics
posted by Helpme .
A car travels 12 km West, 18 km South. What is the total car displacement? The car takes 10 minutes to travel from each initial position to final position. What is the average speed and velocity?

Since the two trip segments are perpendicular, total displacement is sqrt[12^2 + 18^2] = 21.63 km
Divide than by 1/3 hour for the average velocity, 64.9 km/h. The velocity direction is 56.3 degrees south of west (arctan 1.5)
The average speed is the distance travelled (in any direction) divided by 1/3 hour, or 30 km/(1/3) = 90 km/h 
Could you pleas explain it further? Thanks ;)

What don't you understand?

what will i divide by 1/3? And why should I divide it by 1/3?

And where did you get 64.9? Is that the velocity or what?

Divide the displacement (21.63 km) by 1/3 hour, to get the velocity. 1/3 hour is the twenty minutes elapsed time. You presumably want the velocity in km/h, so time must be in hours, not minutes.
The result of the division to get average velocity will be 64.9 km/h, as indicated.
Average velocity is displacement diovided by the time interval.