Jack and jill exercise in a 25.0-m-long swimming pool. jack swims nine lengths of the pool in 2 minutes and 19.5 seconds, while jill, the faster swimmer, covers ten lengths in the same time interval. find the average velocity and average speed of each swimmer.

First of all, the average speed and average velocity would just have the same magnitude, so they are equal. Now, the average speed or average velocity is the total distance traveled divided by the elapsed time. For consistency of units, let's convert the time to seconds.

Time for Jack or Jill = 2 min(60s/1min) + 19.5 s = 139.5 seconds

Then, the average speed for each would be:
Average speed of Jack = 9(25 m)/139.5 s = 1.613 m/s
Average speed of Jill = 10(25 m)/139.5 s = 1.792 m/s

Work is reduced while time is decreased