An athelete swims from northend to southend of a 50.0m pool in 20.0s and makes the return trip to the starting position in 22.0s a) what is the average velocity for the first half of the swim? b) what is tje average velocity for the second half of the swim? c) what is the average velocity for the roundtrip?

Average velocity =

    (distance between start-point and end-point) / (time from start to end)
in the direction of
    (direction from the start-point to the end-point) .

a).  The average velocity for the first half is

                             (50m)/(20sec) = 2.5 m/s south.

b).  The average velocity for the second half is 

                            (50m)/(22sec) = 2.273 m/s north

c).  Average velocity for the round trip is zero, because
the start-point and end-point are the same point.

However ...

Average SPEED = (total distance covered) / (time to cover the distance)

Average SPEED for the round trip is 

                 (100 m) / (42 sec) = 2.381 m/s  (rounded)