On your way to class one morning, you leave home and walk at 3 m/s east towards campus. After exactly one minute you realize that you've left your physics assignment at home, so you turn around and run, at 6 m/s, back to get it. You're running twice as fast as you walked, so it takes half as long (30 seconds) to get home again.

Note that you covered 180 m before turning around.

Analyzing the 90 second out-and-back trip, what is your average speed?

1. zero (0/28) (0%)
2. 2 m/s (3/28) (11%)
3. 4 m/s (13/28) (46%)
4. 4.5 m/s (11/28) (39%)
5. 5 m/s (1/28) (4%)

Average speed is the total distance covered divided by the total time.
That works out to 360 m / 90 s = 4 m/s

What is your average velocity?

1. zero (20/34) (59%)
2. 1.5 m/s West (1/34) (3%)
3. 3 m/s West (5/34) (15%)
4. 4 m/s West (6/34) (18%)
5. none of the above (2/34) (6%)

Average velocity is the net displacement divided by the total time.
Since the net displacement is zero, v_avg = 0.