Physics
posted by Sarah .
A runner covers one lap of a circular track 40.0 m in diameter in 62.5s (a) for that lap what were her average speed and average velocity? (b) if she covered the first half lap in 28.7 s, what were her average speed and average velocity for that half lap?

speed=distanceran/time
velocity=(final positioninitialposition)/time
I assume you know the distance around a circle (PI*diameter). 
what do you mean by final position  initial position

The final  initial positions in part b are on opposite sides of the circle. For distance run, you went half way around the track. (pi D/2)
For distance between beginning point and end point you do not go around the track, you draw a vector straight across from start to finish, thus just the diameter.(D)
In part a, your average velocity was ZERO, because your final position is the same as your initial position and you went nowhere. Of course your speed was pi D/62.5