1. Because the runway is circular, when they first met, the distance they walked added up to exactly one circle (you can draw a picture).

Suppose we meet for the first time in t minutes, then

350 tons +250 tons = 400

T= 400/(350+250) = 2/3 minutes, that is, 40 seconds.

When they meet again, the distance they traveled adds up to a circle, so it is the same as the time calculated above, that is, they meet again after 40 minutes.

2. This is very flexible, such as finding the number of loneliness in other continents in 2002 (or 20 10).