The equal relationship is: the sum of the distances traveled by two people = the distance between them at the beginning.

The pursuit problem is characterized by:

The equal relationship is: starting at the same time and in different places: the difference between the distances traveled by two people = the distance between them at the beginning.

Navigation problems: downstream speed = (still water ship speed+current speed) and upstream speed = (still water ship speed-current speed)

When someone rides a bike, he should go to the railway station from home within the specified time. If his speed is15km per hour, he can arrive 24 minutes earlier. If his speed is 12km/h, then he is 15 minutes late. What is the stipulated time? How far is his home from the railway station? 15km/h = 250m/min， 12km/h = 200m/min(250×24+200× 15)÷(250-200)= 180min = 3。