Analysis: When they met for the first time, the distance from the midpoint of A and B was 100m, indicating that they walked 400m and 600m respectively. When they met for the second time, they walked two full distances, namely 800m and 1 200m, so they walked three full distances.

Column type:

( 1000/2+ 100)*3- 1000- 1000/2

=600*3- 1000-500

=300 meters

A: The second meeting between them is 300 meters from the midpoint.