A100-meter sprint is a race using only the straight side of a racetrack. a 400-meter sprint is a race that makes one complete lap around a racetrack. why are velocity and speed the same for a 100-m sprint but not a 400-m

For 100m Race ,
displacement = distance covered .
divide the above equation by time t (assuming it takes t time to complete 100m race),
we get,
velocity = speed.
and for 400m race 1 lap is completed this means that racer's initial and final position coincide (or same) hence,
displacement = 0,
distance ≠0=400m.
=> displacement ≠distance.
=> velocity ≠ speed.

Maybe you should get some from your teacher and learn more so you can get your grades up and maybe study a bit more